Basic Food Safety for Health Workers M

Home , Amatoxin, Penitrem A, Solanine, Toxic oil syndrome

WHO/SDE/PHE/FOS/99.1 Distr.: General Original: English

World Health

Geneva 1999 Organization

Basic Food Safety for Health Workers M. Adams and Y. Motarjemi

WHO Basic Food Safety for Health Workers

Contents

Acknowledgements ...... 1 Introduction ...... 3 Chapter 1

Foodborne illness ...... 5 Food in health and disease ...... 5 Extent of foodborne illness ...... 8 Foodborne illness: its definition and nature ...... 10 Infection ...... 11 Intoxication ...... 11 Infectious dose ...... 12 Health consequences of foodborne illness ...... 13 Economic impact of foodborne illness ...... 16 Chapter 2

Foodborne hazards ...... 17 Biological hazards ...... 17 Parasites ...... 17 Viruses ...... 18 Bacteria ...... 18 Chemical hazards ...... 18 Industrial pollution of the environment ...... 20 Agricultural practices ...... 21 Food processing ...... 22 Natural toxicants in foods ...... 23 Biological sources ...... 24 Mycotoxins ...... 24 Algal toxins ...... 26 Physical hazards ...... 27 Contents

Chapter 3

Factors leading to microbial foodborne illness ...... 29 Contamination - how do microorganisms get into food? ...... 29 Microorganisms that occur naturally in foods (indigenous microflora) ...... 30 Natural inhabitants of the environment ...... 30 Polluted environment: insanitary practices in agriculture and aquaculture ...... 31 Water ...... 32 Pests and pets ...... 32 The food handler ...... 32 Equipment, utensils and kitchen practices ...... 33 Growth ...... 34 Availability of nutrients ...... 35 Temperature ...... 35 Acidity/pH ...... 36

Water activity (aw) ...... 37 Oxygen (air) ...... 38 Antimicrobial agents ...... 38 Time ...... 38 Survival ...... 39 Major factors leading to foodborne illness ...... 41 Chapter 4

Hazards associated with different foods and their control ...... 43 Red meat, poultry and their products ...... 43 Eggs and egg products ...... 45 Milk and dairy products ...... 45 Fish, shellfish and fishery products ...... 46 Fruits and vegetables ...... 49 Cereals and cereal products ...... 51 Bottled waters ...... 51 Chapter 5

Technologies for the control of hazards ...... 53 Technologies that prevent contamination ...... 53 Packaging ...... 53 Cleaning and disinfection of equipment and utensils ...... 54 Hygienic design of equipment ...... 55 Technologies that control microbial growth ...... 55 Technologies that remove or kill microorganisms in food ...... 56 Heat treatment ...... 56 Canned foods ...... 57 UHTprocessing/aseptic packaging ...... 58 Ionizing irradiation ...... 59 Ultraviolet irradiation ...... 59 Washing and disinfection ...... 59 Basic Food Safety for Health Workers

Chapter 6

Hygiene in food preparation ...... 61 Physical factors: premises and equipment ...... 62 Operational factors: hygienic handling of food ...... 63 Personal factors: personal hygiene and training ...... 64 The Hazard Analysis and Critical Control Point (HACCP) system ...... 65 Chapter 7

The role of health workers in food safety ...... 69 The curative role ...... 69 The preventive role: controlling foodborne hazards ...... 69 Domestic food handlers ...... 70 Expectant mothers ...... 70 Lactating women ...... 70 Mothers of older infants and young children ...... 71 Professional food handlers ...... 71 High-risk groups and people preparing food for them ...... 71 Travellers ...... 71 The elderly ...... 71 The sick ...... 72 The undernourished ...... 72 The community ...... 72 Refugees ...... 72 Schoolchildren ...... 72 Street food vendors and food service establishments ...... 73 Surveillance ...... 73

References ...... 75

Bibliography ...... 77

Appendix 1 Causative agents of foodborne illness ...... 79

Appendix 2 WHO’s Ten Golden Rules for Safe Food Preparation ...... 113

Appendix 3 The Hazard Analysis and Critical Control Point System (HACCP) ...... 115 Contents Basic Food Safety for Health Workers

Acknowledgements

Basic Food Safety for Health Workers has been prepared with a view to strengthening the education and training of health professionals in food safety. The book has been prepared by Drs Martin Adams, School of Biological Sciences, University of Surrey, United Kingdom and Yasmine Motarjemi, Food Safety Programme, World Health Organization. The contribution of Mrs Ann Dale, Mrs Francoise Fontannaz, Annette Enevoldsen, Mr David Bramley, and Mr Anthony Hazzard in the preparation of the book is gratefully acknowledged. The present text is a draft for review and field-testing. The World Health Organization welcomes the comments of health professionals and other readers and users of this document. WHO would like to acknowledge with thanks the financial support of the Opec Fund for International Development, Vienna, Austria, in the production of this book. This book has been developed in collaboration with the WHO Task Force for Cholera Control and the Swiss Disaster Relief Unit, Berne, Switzerland.

1 Introduction

2 Basic Food Safety for Health Workers

Introduction

Foodborne diseases, especially those caused by pathogenic organisms, remain a serious problem in all countries. Diarrhoea is a feature of most of these diseases and up to 70% of all episodes of diarrhoea may result from the ingestion of contaminated food and water. The WHO book Foodborne diseases: a focus for health education underlines the importance of the education of consumers and food handlers, both domestic and professional, in food safety. It urges governments to take the initiative to develop, in collaboration with industries and consumers, a comprehensive, systematic and continuous programme of health education based on modern approaches to food safety. The book also identifies the health care system, particularly the primary health care system, as one of the most important vehicles for health education in food safety. To be able to assume their role in food safety and advise the population on safe food preparation, health workers should know about the epidemiology of the principal foodborne diseases and the sociocultural conditions that encourage them. They should also receive some training in research methodology, especially in the investigation of foodborne disease outbreaks, Hazard Analysis and Critical Control Point (HACCP) studies, and the investigation of sociocultural characteristics of the population. Health workers should also be inspired to take action in their daily work to raise public awareness of food safety, to advise the mothers of small children or pregnant women in safe food preparation, and generally to assist the community in improving food safety.

To facilitate the training of health workers, WHO has developed a training package including this book and an accompanying training manual. The training package is intended for professionals in the

3 Introduction

health and environmental fields, particularly trainers of primary health care workers, physicians, nurses, midwives, nutritionists, medical students, and other professionals who need a basic under- standing of food safety. This book provides an introduction to the basic knowledge that health professionals need in order to discharge their responsibilities in food safety. The book aims to increase the knowledge of health professionals regarding:

l the nature of foodborne diseases and their health and economic consequences;

l the epidemiology of foodborne diseases;

l the role of food in the transmission of various infections and intoxications;

l the factors leading to foodborne diseases;

l the measures necessary to improve food safety. A training manual based upon a problem-solving approach to learning accompanies the present book. It provides direction on expected learning outcomes, summaries of key information to be covered, lists of recommended references and resources required, and suggestions for training activities. It also includes transparency masters and copies of hand-outs.

4 Foodborne illness

society at large. These costs include loss Economic impact of of income by the affected individual, cost of health care, loss of productivity foodborne illness due to absenteeism, costs of investigation of an outbreak, loss of income due What is damaging and distressing at the to closure of businesses and loss of sales level of the individual also has serious when consumers avoid particular prod- implications on a far larger scale. In de- ucts. In 1989 it was estimated that the veloped countries efforts to quantify the total cost of bacterial foodborne illness economic impact of foodborne illness are to the United States economy was US$ comparatively recent, but it is clear from 6,777,000,000. In developing countries, these that foodborne illness is a major where the problem of diarrhoeal disease burden on the economy. Costs arise from is far greater, the effect on economic ac- a number of different sources and are tivity and development can only be far incurred both by the individual and by more severe.

KEY POINTS

l Food is essential for health and well-being.

l Food may also be a cause of illness.

l Foods may be intrinsically toxic or may be contaminated with toxic chemicals or pathogenic organisms.

l Foodborne illness is extensively under-reported.

l Microorganisms (bacteria, viruses, moulds and parasites) are the most important cause of foodborne illness.

l Bacteria are generally most important.

l Most foodborne illness is associated with gastrointestinal symptoms of nausea, vomiting, stomach pains and diarrhoea.

l Foodborne illness is caused by two mechanisms: infection and intoxication.

l The infectious dose varies between organisms and between individuals.

l Foodborne illness can have seriously damaging effects on individuals, particularly young children, and on society as a whole.

16 Basic Food Safety for Health Workers

t t

Food Contamination Diarrhoea Malnutrition t á Death t

Figure 1.3 The malnutrition and diarrhoea cycle

15 BC - Bronchitis BN - Bronchopneumonia 14 CEL - Cellulitis CONJ - Conjuncivitis Normal growth curve 13 D - Diarrhoea FUO - Fever of unknown origin 12 I - Impetigo M - Measles 11 S - Stomatitis URI - Upper respiratory illness 10 D 9 Child’s growth curve URI D D URI D URI S D 8 D D BN URI BC D URI D D 7 CEL D FUO BC URI URI

Body weight in KG D D D D D D D BC 6 D URI M BC URI URI 5 D I 4

3 CONJ I 2

0 3 6 9 12 15 18 21 24 27 30 33 36 Age in months

Source : Mata, LJ Nutrition and infection. Protein Advisory Group bulletin (1971) Figure 1.4 Growth pattern of a child with frequent episodes of diarrhoea and other infections (The horizontal bars indicate the duration of the infectious disease)

15 Foodborne illness

Table 1.7 Examples of secondary disease state resulting from foodborne infections Disease Associated complication Brucellosis Aortitis, orchitis, meningitis, pericarditis, spondylitis Campylobacteriosis Arthritis, carditis, cholecystitis, colitis, endocarditis, erythema nodosum, Guillain-Barré syndrome, haemolytic-uraemic syndrome, meningitis, pancreatitis,septicaemia E.coli (EPEC & EHEC types) Erythema nodosum, haemolytic-uraemic syndrome, infections seronegative arthropathy Listeriosis Meningitis, endocarditis, osteomyelitis, abortion and stillbirth, death Salmonellosis Aortitis, cholecystitis, colitis, endocarditis, orchitis, meningitis, myocarditis, osteomyelitis, pancreatitis, Reiter’s syndrome, rheumatoid syndromes, septicaemia, splenicabscess, thyroiditis Shigellosis Erythema nodosum, haemolytic-uraemic syndrome, peripheral neuropathy, pneumonia, Reiter’s syndrome, septicaemia, splenic abscess, synovitis Taeniasis Arthritis Toxoplasmosis Foetus malformation, congenital blindness Yersiniosis Arthritis, cholangitis, erythema nodosum, liver and splenic abcesses, lymphadenitis, pneumonia, pyomositis, Reiter’s syndrome, septicaemia, spondylitis, Still’s disease Source: Mossel, 1988.

foodborne microorganisms (Table 1.7). In for more than 15% of their young lives. an outbreak of salmonellosis in Chicago The immediate cause of death from in 1985, caused by contaminated pasteur- diarrhoeal disease is usually the dehydra- ized milk, more than 2% of the 170,000- tion that results from the loss of fluid and 200,000 people infected suffered from electrolytes in diarrhoeal stools, but di- reactive arthritis as a result of their in- arrhoea can also have other serious fection (3). Guillain-Barré syndrome is a health consequences. It may lead to mal- serious and potentially life-threatening nutrition since food intake is reduced ei- neurological disease characterized by ther as a result of loss of appetite or the acute weakness, autonomic dysfunction withholding of food, and those nutrients and respiratory insufficiency. It is a that are ingested are poorly absorbed or chronic sequela associated with acute simply lost by being swept out with the gastrointestinal infection particularly by diarrhoeal stools. Malnutrition in its turn Campylobacter jejuni. can predispose children to longer episodes of diarrhoea as well as other infections, In developing countries, diarrhoeal aggravating the problem still further. This diseases, particularly infant diarrhoea, are can result in a downward spiral of increas- a major public health problem. It has ingly poor health which, unless it is bro- been estimated that annually some 1500 ken in some way, will lead ultimately to million children under five years of age premature death (Figure 1.3). Even where suffer from diarrhoea and over 3 million this does not proceed inexorably to a fa- die as a result (4). Individual children ex- tal end, the physical and mental growth perience on average 3.3 episodes of di- of the child is severely impaired. This is arrhoea each year, though in some areas shown in Figure 1.4 which records the the number of episodes may exceed 9 and effect of repeated bouts of diarrhoea and children can be suffering from diarrhoea other illnesses on a child’s development.

14 Basic Food Safety for Health Workers differ appreciably. Shigella and limiting indispositions that are restricted enterotoxigenic E. coli (ETEC) are oth- to gastroenteritis and are not usually life- erwise very similar organisms but esti- threatening. Exceptions occur with par- mates of their respective infective doses ticularly susceptible individuals such are markedly different, reflecting differ- as the very old or very young, pregnant ences in their virulence. women or those who are already very sick Susceptibility to infection can vary with or weak for some other reason. These a range of factors such as age, general vulnerable groups constitute quite a large health, nutrition, immune status and proportion of the population and for whether a person is undergoing medical many of them diarrhoeal disease can be treatment. Listeriosis can be mild or even fatal. asymptomatic in some individuals but A number of foodborne pathogens such can be severe and often life-threatening as Clostridium botulinum are also associated in the unborn child. In people with low with acute extraintestinal (systemic) gastric acidity, increased survival of disease. C. botulinum causes a severe ingested pathogens can reduce the neuroparalytic syndrome which is often required infective dose, thereby fatal. The mortality rate in outbreaks in increasing the risk of infection. This is the United States between 1976 and 1984 often found in the elderly and may help was 7.5% but it can be substantially explain their increased susceptibility to higher (3). Survival in cases of botulism foodborne infections. The food that is the is critically dependent on early diagnosis vehicle of infection may also help reduce and treatment. the infectious dose by protecting the Sometimes extra-intestinal disease pathogen from the lethal effect of the transmitted by food is particularly stomach’s acidity. This has been noted associated with certain susceptible indi- particularly with fatty foods such as sa- viduals. For example, infection by Liste- lami, cheese, chocolate and ice cream ria monocytogenes can vary from a mild, flu- where low numbers of salmonella have like illness to meningitis and been implicated in foodborne disease meningoencephalitis. It is particularly outbreaks (Table 1.6). serious in pregnant women; the mother Where the infectious dose is high, the may experience relatively mild symptoms food vehicle can play a very specific role but infection of the fetus can result in in the illness. Depending on the food’s abortion, stillbirth or premature labour. composition and conditions of storage, Listeriosis is also more than 300 times a pathogen present at low and possibly more common in AIDS patients than in harmless levels may grow to numbers the general population. Cancer patients sufficient to produce illness. The speed and other immunocompromised with which bacteria can grow is described individuals are subject to bacteraemia in more detail in Chapter 2. caused by foodborne bacteria. Verotoxin- producing E. coli generally results in a bloody diarrhoea but can cause the Health consequences haemolytic uraemic syndrome, characterized by thrombocytopaenia, of foodborne illness haemolytic anaemia and acute kidney failure, particularly in children. For most adults in the industrialized world, incidents of foodborne illness are Some chronic diseases, particularly ar- unpleasant but are generally mild and self- thritic conditions, can be triggered by

13 Foodborne illness

Since the toxin is ingested with the food This is probably still true in many cases, there is no direct person-to-person spread, but it has been shown more recently that as can occur with some enteric infec- food may also be the vehicle of tions, and the incubation period (the time contamination in up to 70% of cases. between consumption of the food and To cause illness, a sufficient number of the appearance of symptoms) tends to cells must be consumed. This is known be shorter, generally of the order of one as the infectious dose. The infectious or two hours or even less in some cases. dose varies from one organism to another This is because the toxin begins to act as and from person to person. For soon as it reaches the site of action, Campylobacter jejuni the infectious dose is whereas with infections the microorgan- thought to be quite low, while relatively isms need time to multiply in the body. high numbers of non-typhoid Salmonella There are some similarities here with other are normally required to produce illness. biotoxins such as mycotoxins and algal Experiments have been conducted where toxins, though algae differ from toxigenic volunteers have consumed different lev- bacteria and moulds in that they do not els of pathogens in order to determine multiply in the food. Also, the health ef- the infectious dose. These results and data fects of mycotoxins tend to be long-term from the investigation of actual rather than acute (see Chapter 2). outbreaks give some indication of the numbers of bacteria required to produce illness, but they should be regarded only Infectious dose as a rough guide (Table 1.6). Successful infection is the result of the Infective pathogens can be introduced interaction of two variable factors: the into the body from a variety of sources. virulence of the pathogen (its ability to In the past, it was thought that cause illness) and the susceptibility of the contaminated water was the main source individual. The virulence of different of the pathogens that cause diarrhoea. Salmonella serotypes, for example, can

Table 1.6 Estimated infectious doses

Escherichia coli enteropathogenic 106–1010 enterotoxigenic 106–108 enteroinvasive 108 enterohaemorrhagic 101–103 Shigella 101–102 Salmonella Typhi <103 Other salmonellae 105-107 but: Salmonella Newport 60 – 230 in hamburger Salmonella Eastbourne 10 – 25 in chocolate Salmonella Heidelberg 100 – 500 in cheese Clostridium perfringens 106–108 Campylobacter 500 Vibrio cholerae 106 Vibrio parahaemolyticus 105–107

12 Basic Food Safety for Health Workers the normal functions of the gut are up- through the gut. It then multiplies, colo- set in some way. nizing the surface. In some cases, such The gastrointestinal tract or gut is not an as infection with enteropathogenic Es- internal organ of the body but a tube run- cherichia coli, this produces changes in the ning through it where foods are digested gut epithelium which reduce its absorp- and absorbed, and unwanted waste prod- tive capacity or cause fluid secretion. ucts are expelled. In addition to absorp- Colonizing bacteria can also produce tion of nutrients from foods, absorption enterotoxins; toxins that alter the function and secretion of water are important gut of the cells lining the gut and cause them functions. Water absorption normally to secrete water and electrolytes into the exceeds secretion. Each day, a typical intestine to produce a profuse watery adult will ingest about two litres of wa- diarrhoea. A notable example of this is ter. To this must be added saliva and se- cholera, but a similar sequence of events cretions from the stomach, pancreas and occurs with enterotoxigenic E. coli liver which altogether make a total of 8- infections. 10 litres entering the small intestine daily. Invasive pathogens are not confined to About 90% of this fluid is absorbed be- the intestinal lumen but can penetrate the fore it enters the large intestine where 80- cells lining the gut. In some cases their 90% of the remainder is absorbed. penetration is limited to the immediate Changes in the small intestine that either vicinity of the gut, as with the non-ty- decrease absorption or increase secretion phoid salmonellas. Some pathogens in- will reduce overall absorption and result vade the mucosa of the large intestine in a larger fluid flow into the large intes- rather than the small intestine, producing tine. If this exceeds the relatively limited inflammation, superficial abscesses and absorptive capacity of the large intestine ulcers, and the passage of dysenteric then diarrhoea occurs. stools containing blood, pus and large amounts of mucus. In other cases, Bacteria cause foodborne illness by two microbial invasion is not restricted to the mechanisms: infection and intoxication. gut’s immediate locality and the organ- The latter can also be caused by chemi- ism spreads further through the body, cal contaminants and naturally occurring producing symptoms other than diarrhoea toxins. at sites remote from the gut itself, as for example in brucellosis, listeriosis, typhoid Infection and paratyphoid fevers. Infection occurs when living bacteria are Illnesses caused by foodborne viruses ingested with food in numbers sufficient and parasites are also broadly similar in for some to survive the acidity of the that viable organisms gain access to their stomach, one of the body’s principal pro- site of action in the body via the tective barriers. These survivors then pass gastrointestinal tract. into the small intestine where they multiply and produce symptoms. Intoxication Infections can be invasive or non-inva- With foodborne intoxications, the bac- sive. In non-invasive infections, the or- teria grow in the food producing a toxin. ganism attaches itself to the gut surface When the food is eaten, it is the toxin, or epithelium to prevent itself from being rather than the microorganisms, that washed out by the rapid flow of material causes symptoms.

11 Foodborne illness

figures are collected, but it is thought to n Changing lifestyles also means that reflect an underlying increase in the food preparation may be in the hands number of cases as well. of the relatively inexperienced as A number of factors have contributed to more mothers go out to work and this trend. Their relative importance var- more people eat pre-prepared foods, ies between countries and between patho- meals from catering establishments or gens but some of the most significant are food from street vendors. as follows: n An increasing proportion of the population is more susceptible to n Increasing industrialization and urban living has meant that the food chain foodborne illness. This includes the has become longer and more complex, malnourished, the elderly, those who increasing opportunities for contami- have some underlying condition such nation. It also means that more peo- as liver disease and those who are ple are likely to be affected by a sin- immunocompromised as a result of gle breakdown in food hygiene. infections such as HIV and immunosuppressive medical treatment. n In poorer countries increased urbani- zation and rapid population growth have not been matched by development of the health-related infrastruc- Foodborne illness: ture, including basic sanitation, and this has led to increased risk of con- its definition and tamination of the food and water supply. nature

n Increasing affluence in other areas has The term “food poisoning” has often been led to greater consumption of foods used in some countries, but it is an ex- of animal origin such as meat, milk, pression that can sometimes be restric- poultry and eggs. These foods are rec- tive or misleading. Foodborne illness or ognized as more common vehicles of foodborne disease are now the generally pre- foodborne pathogens and this situa- ferred terms. Foodborne disease can be tion can be exacerbated by the meth- defined as: ods of intensive production required “any disease of an infectious or toxic to supply a larger market. nature caused by or thought to be n There is greater international move- caused by the consumption of food ment of both foods and people. Ex- or water”. otic Salmonella serotypes have been Though there are a number of important introduced into Europe and the exceptions that will be described later, United States as a result of the im- in most cases and in most people’s minds, portation of animal feeds. A number the illnesses caused by foodborne micro- of outbreaks of illness associated with organisms, principally bacteria, are asso- imported foods have also been re- ciated with gastrointestinal symptoms of corded. Tourism is one of the world’s nausea, vomiting, stomach pains and di- major growth industries and every year arrhoea. Since diarrhoea is a common more and more people travel abroad clinical symptom in foodborne diseases, where they are exposed to increased many of these diseases are referred to as risk of contracting foodborne illness. “diarrhoeal diseases”. These occur when

10 Basic Food Safety for Health Workers foodborne in origin or may not be re- cases being reported. Studies in some ported to the relevant authority for re- countries point to an under-reporting cording. Estimates vary but it is gener- factor of up to 350 in some cases. ally believed that in developed countries less than 10%, or even only 1%, of cases Statistics from both developed and de- of foodborne illnesses ever reach official veloping countries show an increasing statistics. In countries with fewer re- trend in foodborne illness over recent sources, under-reporting must be even years (Figure 1.2). In part, this is prob- greater, with probably less than 1% of ably due to improvements in the way the

90000

80000

70000

60000 Notifications 50000

40000

30000 1989 1990 1991 1992 1993 1994 1995 1996 Year Figure 1.2a Foodborne illness : annual notifications, England and Wales

180

140

120

100

40 Cases per 100,000 population 20

0 1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 Year

Figure 1.2b Incidence of foodborne disease in Venezuela

9 Foodborne illness

DDT complex (DDT and its degradation products) contaminates food mainly as a result of its earlier use in agriculture and public health. While DDT is now banned in most countries for agricultural uses, the persistence and fat solubility of DDT have resulted in widespread contamination of the food chain. Levels of DDT in breast milk reflect the exposure of the mother to DDT and is a good indicator of the levels of DDT in the food supply. Breast milk is also the sole food for the first few months of life and dietary intake of DDT complex by infants in some countries approaches or exceeds the WHO recommended provisional tolerable intake of 20 mg DDT/kg body weight/day. Source: GEMS/Food WHO document (WHO/FSF/FOS/97.9) Figure 1.1 Dietary intake of DDT by infants from human milk

Data collected by the Food Contamina- A number of human viruses can be trans- tion Monitoring and Assessment Pro- mitted by food and human diseases gramme (GEMS/Food) indicate that in caused by protozoa, helminths and nema- many countries the trend in chemical todes that are animal parasites are prob- contaminant levels is generally down- lems of emerging importance in a wards. This is most apparent in developed number of countries. These differ from countries where exposure to these most bacterial foodborne illnesses in that contaminants is often much lower than the causative organism does not multi- in developing countries (Figure 1.1). ply in the food itself. A brief description Factors contributing to this disparity are of the major foodborne pathogens and discussed in Chapter 2. The general over- some of their key features is presented all improvement is due to increased re- as Appendix 1. Most of the following is striction of the use of toxic chemicals concerned primarily with bacterial patho- and pesticides that persist in the environ- gens, though specific aspects of other ment, and improved control of environ- pathogens are mentioned where appro- mental pollution. Available data on priate. foodborne illness of biological origin provide a strong contrast to this reduction in chemical contamination. Extent of foodborne Several different types of organism can cause foodborne illness. Bacteria, single- illness celled organisms with typical dimensions of around 1mm (10-6m), are the most im- Many developed countries have sophis- portant and well studied foodborne ticated systems for collecting data on the pathogens. A key factor is their ability to incidence and causes of foodborne illness. multiply in food, thus increasing the haz- Yet it is known that these data represent ard they pose. This is discussed in Chap- only a fraction of the number of cases ter 2. Filamentous fungi (moulds) can also that occur. Infected individuals may not grow in foods and some produce toxic seek medical advice, and if they do their substances called mycotoxins. illness may not be recognized as

8 Basic Food Safety for Health Workers

Table 1.4 Mean daily intakes (mg) of natural food toxicants Class of compound (food source) Population Total Vegetarian

Glucosinolates (brassicas) 50 110 Glycoalkaloids (potatoes) 13 70 - 90 Saponins (legumes) 15 100 (*220) Isoflavones (soya) <1 105

* U.K. vegetarian population of East African origin Source: Morgan, MRA. and Fenwick, GR National foodborne toxicants. Lancet, 15 December 1990, p. 1492/1495. In most cases foods are not contaminated with pesticide residues, environmental intentionally but rather from carelessness chemical contaminants and the use of food or insufficient education or training in food additives cause most concern. Yet experi- safety. In some cases, contamination may ence shows that most outbreaks of be deliberate as, for example, in the mis- foodborne disease are associated with use of food additives such as prohibited microbiological contamination. colouring. In one serious case in Spain, con- This is reflected in the available statistics taminated industrial rapeseed oil was sold on the etiology of foodborne illness. for human consumption, killing more than (Table 1.5). One study estimated that 500 people and crippling more than 20,000 people are 100,000 times more likely to (1). become ill as a result of microorganisms How the relative importance of these haz- in food than as a result of pesticide ards is perceived depends on who you ask. residues (2). Surveys indicate that, as far as the general public is concerned, hazards associated

Table 1.5 Etiology of foodborne disease outbreaks (with known etiology) in Latin America and the Caribbean, 1995-1997 Etiological agent Percentage Percentage of cases involved of outbreaks in outbreaks Bacteria 46.3 83.03 Of which: Bacillus cereus 1.3 1.2 Clostridium perfringens 4.2 4.1 Clostridium botulinum 0.4 0.1 Escherichia coli 11.4 7.8 Salmonella 37.0 43.1 Shigella spp. 3.1 21.9 Staphylocccus aureus 36.6 19.5 Vibrio cholerae 4.2 0.9 Vibrio parahemolyticus 0.2 0.4 Other 1.6 1.0 Total 100.0 100.0 Viruses 1.8 3.7 Parasites 1.8 2.9 Marine toxins 44.2 8.0 Plant toxins 0.4 0.1 Chemical substances 5.4 2.3 Total 100.0 100.0 Source: Adapted from data provided by the Pan American Institute for Food Protection and Zoonoses, INPPAZ, PAHO/ WHO 1998

7 Foodborne illness

Table 1.2 Examples of vitamin and mineral deficiency syndromes

Micronutrient Deficiency syndrome A Night blindness, xeropthalmia Thiamine Beriberi, Wernicke’s encephalopathy; Korsakoff’s psychosis Niacin Pellagra Riboflavin Mucosal lesions Pyridoxine Glossitis, neuropathy Folate Megaloblastosis, villus atrophy

B12 Pernicious anaemia, megaloblastosis, neuropathy C Scurvy D Rickets, osteomalocia K Hypoprothrombinaemia Iodine Goitre, cretinism Iron Anaemia

and established processing and handling Other foodborne hazards can be described procedures are followed, the majority do as extrinsic, indicating that their presence not cause serious problems. Natural food is a result of contamination of the food. toxins are described in more detail in This includes contamination with indus- Chapter 2 but a few examples are given trial chemicals or pesticide residues, right in Table 1.3 and estimates for some mean through to the presence of pathogenic bac- daily intakes in the United Kingdom are teria or parasites. The range of possibili- presented in Table 1.4. ties is summarized in Table 1.3. Table 1.3 Causes of foodborne illness Examples INTRINSIC HAZARDS (Natural Toxins or Antinutritional Factors) oxalic acid (rhubarb, spinach) alkaloids solanine (potatoes) dioscorine (yams) cyanide (cassava, lima beans) haemagglutinin (red kidney beans) protease inhibitors (legumes) phytic acid (bran) amatoxin, psilocybin and others (toxic mushroom) EXTRINSIC HAZARDS Chemical Contamination dioxins, PCBs heavy metals cadmium mercury lead pesticide residues Biological Contamination Bacteria causing infection e.g. Salmonella causing intoxication e.g. C. botulinum Parasites helminths e.g. roundworms protozoa e.g. Giardia lamblia Viruses e.g. Hepatitis A, Small Round-Structured Viruses (SRSVs) Fungi/mycotoxins e.g. aflatoxin Algae (e.g.dinoflagellates leading to paralytic shellfish poisoning)

6 Basic Food Safety for Health Workers

Chapter 1 Foodborne illness

Food in health and disease

Food is essential both for growth and for Even when a diet provides enough pro- the maintenance of life. It supplies the tein and energy, it may not supply suffi- energy and materials required to build cient essential minerals or vitamins and and replace tissues, to carry out work and may thus give rise to characteristic defi- to maintain the body’s defences against ciency disorders (Table 1.2). disease. Illness can also result from what a food Food can also be responsible for ill-health. contains rather than from what it lacks. Failure to consume enough of the right kind Some hazards of this kind are described of food will impede growth and impair as being intrinsic to the food in the sense health. For example, protein-energy that they are normal and natural constitu- malnutrition can lead to a range of clinical ents of the food. Many common food manifestations. These vary from marasmus, plants, for instance, contain toxic com- where consumption of protein, dietary pounds designed to deter predators or energy and other nutrients are chronically invading microorganisms. Their intake is reduced, to kwashiorkor (sometimes inevitably higher in those people with a thought to be associated with an over- largely vegetarian diet. reliance on low protein staples) which results in a quantitative and qualitative However, in most cases where the food deficiency of protein (Table 1.1). supply is generally varied and plentiful,

Table 1.1 Classification of severe protein-energy malnutrition in children Weight for age* With oedema Without oedema 60 –80% Kwashiorkor Undernutrition Less than 60% Marasmic kashiorkor Marasmus

* As % of standard (National Centre for Health Statistics) weight Source: Tomkins, AM Nutrition in clinical medicine. In: Textbook of Medicine. RL Souhami and J Maxham (eds) 2nd edn. Churchill Livingstone, Edinburgh, 1994: p.106.

5 Basic Food Safety for Health Workers

Chapter 2 Foodborne hazards

Biological hazards

The overriding importance of microor- Parasitic worms have complex life cycles ganisms in foodborne illness has already where some time is spent in the tissues been mentioned. Details of individual of an animal host (Figure 2.1). They do organisms are presented in Appendix 1. Here we briefly introduce the different types of organism responsible and then consider some general features associated with the transmission of microbial foodborne illnesses, particularly those caused by bacteria.

Parasites These include protozoa and helminths (worms). Though considerably larger and more complex than other organisms conventionally classified as microorganisms, such as bacteria and viruses, it is often convenient to consider parasites under the same heading. Para- sites can cause a variety of illnesses ranging from diarrhoea to liver cancer. Infection with diarrhoeagenic protozoa such as Giardia lamblia and Entamoeba histolytica is normally the result of faecal contamination of a food or water source and direct person-to-person spread can occur. These protozoa can be killed by thorough cooking. Other protozoa such as Toxoplasma gondii and Sarcocystis hominis can infect the tissues of meat animals and Figure 2.1 Life cycle of the liver fluke, be transmitted by undercooked meat. Fasciola hepatica

17 Foodborne hazards

not show any marked heat resistance and illness. The individual organisms and the transmission to humans is usually the re- illnesses they cause are described in Ap- sult of consumption of undercooked fish pendix 1. Specific aspects of bacterial or meat. Some like the liver fluke Fas- behaviour and foodborne illness feature ciola hepatica, however, spend part of their prominently in Chapter 3. life cycle in a water snail from which it is released to contaminate aquatic plants which may then be eaten by humans. The pork and beef tapeworms Taenia solium and T. saginata respectively are widely Chemical hazards distributed; in the Democratic Republic of Congo, Ethiopia and Kenya, more For many chemical contaminants, a low than 10% of the population are infected level of consumption is both unavoidable with T. saginata. In the former Yugosla- and harmless. Various national regulatory via up to 65% of children were found to authorities and international bodies, such harbour the organism (5). Foodborne as the Joint FAO/WHO Expert trematode infections are a severe prob- Committe on Food Additives (JECFA), lem the extent of which is only just have established threshold values for in- emerging (Figure 2.2). dividual additives and contaminants below which there is no appreciable risk. Viruses These levels of acceptable daily intake (ADI) or provisional tolerable daily (or Viruses are very simple organisms that weekly) intake are expressed as the cannot replicate outside a susceptible number of milligrammes of the chemical host cell and do not therefore multiply in which may be safely consumed by a hu- foods. Food and water can, however, be man for each kilogramme of the consum- the vehicle for transmission of a number er’s body weight. They are usually derived of different viruses that infect humans from experiments in animals which de- via the gastrointestinal tract. This is in- termine the level at which the chemical variably the result of contamination of has no adverse effect on the animal. This food by faeces or vomitus from an in- is known as the no-observed-adverse-ef- fected individual, possibly via some infect level (NOAEL). The NOAEL for the termediary vehicle such as water or most sensitive animal species is then di- equipment. vided by a safety factor, usually 100, to Poliomyelitis and hepatitis A are the most arrive at the ADI. Bodies such as the Joint serious viral diseases that are known to FAO/WHO Meeting on Pesticide be transmitted by this route; Hepatitis E, Residues (JMPR) evaluate pesticide which can be waterborne, is a significant residues and recommend ADIs and maxi- cause of infectious hepatitis in Asia and mum residue levels. Since its inception Africa. There are also a number of food in 1962 the Joint FAO/WHO Codex and waterborne viruses that cause diar- Alimentarius Commission has adopted rhoea, most notably the small round- more than 3200 maximum residue levels structured viruses or Norwalk-like agents for various pesticide/commodity combi- and Rotavirus. nations. Maximum residue levels are also prescribed for a number of veterinary Bacteria drugs. Bacteria are generally considered to be Chemical hazards in foods can arise from the most important agents of foodborne a number of different sources.

18 Basic Food Safety for Health Workers

Figure 2.2

Foodborne trematode infections: the global distribution is changing with the environment and human behaviour

19 Foodborne hazards

Industrial pollution The most serious outbreak of mercury intoxication where industrial wastes con- of the environment taminated fish occurred at Minimata Bay Modern industry produces huge numbers in Japan some years ago. Over 20,000 of chemical products and by-products. people are thought to have been poisoned These can contaminate the environment since the outbreak was first recognized and food chains, ultimately contaminat- in 1956. Thirteen years later, fish in the ing the human food supply itself. Most bay still contained 50mg Hg/kg body attention in this area has focused on weight compared with the Codex heavy metals such as mercury, cadmium recommended limit of 0.5mg Hg/kg. In and lead, and organics such as the Minimata case, contamination came polychlorinated biphenyls (PCBs). All are from a single source but large quantities now widespread in the environment of mercury are also released from fossil though their concentrations are usually fuel combustion, smelters and low, except in cases of industrial acci- incinerators that can contaminate aquatic dents and environmental disasters. systems via the air. One example of this was when fish in lakes in northern Mercury, for example, has numerous in- Wisconsin in the USA were found to dustrial applications but also has toxic contain levels higher than 0.5mg/kg effects on animals and human beings, though they were remote from obvious particularly pregnant women, nursing sources of contamination. mothers and children. The most toxic form of mercury is methylmercury which Lead is a cumulative poison that affects damages the central nervous system. It the blood-forming tissues and the nerv- is often found in fish since industrial ous and renal systems. Children are most effluents containing mercury are susceptible and adverse effects on intelli- discharged into rivers or seas where the gence and behaviour have been seen with mercury is converted into methylmercury only very low levels of lead in the blood. by bacteria. It then moves up the food Lead can be introduced into the environ- chain and concentrates in the bodies of ment by industry or in exhaust fumes from fish. The ability of contaminants or toxins vehicles using leaded fuel. Sometimes the to concentrate as they pass up the food chemistry of the soil itself can give rise to chain is seen in numerous other instances. contamination problems. A local cooking Pesticide accumulation is illustrated in salt used by some villagers in Nigeria was Figure 2.3. found to contain very high levels of lead

Eat Eat Eat

Source: Hegarty, V Nutrition, Food and the Environment St Paul Minnesota USA, Eagan Press, 1992: p. 33

Figure 2.3 Bioconcentration of environmental chemicals in the food chain

20 Basic Food Safety for Health Workers

(437 mg/kg) and manganese (2340 mg/kg) developing countries, where DDT for compared to common salt (1 mg lead/kg instance is still widely used in the fight and 8.7 mg manganese/kg). Lead, silver against malaria. Residue levels in foods and iron had been mined in the region and from developing countries are generally it was thought that the local geology led higher, but data are not available from to high levels of these elements in the many countries. natural spring from which the salt was re- Organochlorine pesticides have increas- covered (6). ingly been replaced by organophospho- PCBs were manufactured for industrial rus compounds. These do not persist in applications such as use in hydraulic the environment or animal tissues for long systems, transformers and heat periods and survey data have shown that exchangers though their production has they are seldom present in foods. How- been drastically reduced in many ever, they pose a serious health risk when countries since the 1970s. Contamination ingested at high concentrations. of edible oil with PCB has caused large- In a study of 63 outbreaks of intoxica- scale poisonings in Japan and Taiwan and tion due to pesticides (8) four causes of exposure to PCB in the workplace has food contamination were identified: been associated with an increased risk of cancer. Exposure of women to PCBs n Contamination during transport or storage during pregnancy appears to have a long- Typical cases involved powders such term impact on the intellectual function as sugar or flour which were trans- of their children (7). Fish generally con- ported or stored with a pesticide or in tain higher levels of PCBs than other a place previously contaminated with types of food. Information on dietary pesticide. exposure to PCBs is almost exclusively from industrialized countries but the n Ingestion of seed dressed for sowing basic trend has been downwards since the Mainly associated with organic mer- 1970s. cury fungicides, such outbreaks occurred particularly during times of Agricultural practices food shortage when treated seeds were distributed after farmers had already Foods can also carry residues of sown their own grain. Local people pesticides and veterinary drugs. were unable to read the warning label Organochlorine pesticides such as DDT, on the bags or mistakenly believed aldrin and dieldrin were identified in the that washing off the dye also removed early 1970s as a particular problem since the pesticide. they persist in the environment, accumulate in the fatty tissues and n Mistaken use in food preparation increase in concentration as they pass up This occurs when pesticides are mis- the food chain (Figure 2.3). Contamina- taken for food materials such as sugar, tion is particularly associated with foods salt and flour. such as milk, animal fats, fish and eggs. As a result of concerns over their poten- n Misuse in agriculture tial carcinogenicity and harm to the en- Pesticides have been found in food or vironment, the use of organochlorine water due to misuse near harvesting pesticides has been restricted in many time, misuse of containers, countries and residue levels in foods have contamination of ground water and shown a decline over recent years. They use of excessively high doses in do however remain important in many agriculture.

21 Foodborne hazards

Residues of veterinary drugs such as an- foods stored in inadequately glazed earth- tibiotics can also find their way into milk enware pots. When pots are glazed at or meat. In many cases the long-term ef- temperatures below 1200oC, much of fects of these on human health are not the lead in the glaze will remain soluble known but they can, for example, pro- and if the pots are used to store acidic voke strong allergic reactions in sensitive foods such as pickles or fruit juices then people. They can also encourage the the product can become contaminated. spread of antibiotic resistance in bacte- Apple juice that caused a fatal case of ria, making treatment of human infection lead poisoning contained 1300 mg/l lead more difficult, and for this reason it has after three days storage in such a jar (10). been recommended that antibiotics used Chemicals have been deliberately added in human medicine should not be used to foods since the earliest times. Before in animals. Antibiotic residues in milk the advent of accurate analytical meth- that is used to produce fermented prod- ods this was largely uncontrolled and ucts can interfere with the fermentation open to abuse, but nowadays their use is process by inhibiting the desirable lactic subject to much closer regulation. Food acid bacteria. Normally this is just a tech- additives can serve a number of purposes, nical problem resulting in economic loss such as preservative, antioxidant, acidity but, when it occurs, pathogens present regulator, emulsifier, colour, flavour or in the milk may grow and pose a health processing aid. The health implications hazard later. For these reasons many of additives is constantly under review countries have regulations prohibiting the by national regulators and international sale of milk from cows being treated for bodies such as JECFA who recommend mastitis and milk is routinely tested for ADI levels on the basis of data from the presence of antibiotic residues. toxicological studies. Additives such as A few hormonal agents are used for some food colourings have occasionally growth promotion in farm animals (e.g. been banned as a result of such studies. bovine somatotropin hormone, or BST). Where additives are allowed, permitted Minute residues of these drugs do not levels of use are prescribed for specified pose a risk for consumers, although there foods. Occasional problems may arise, are different opinions on the acceptability however, with unscrupulous or ill- of these drugs and monitoring is informed food processors who use non- necessary to ensure that permitted limits permitted additives such as boric acid or are not exceeded. excessive levels of permitted ones. Food processing Nitrates and nitrites occur naturally in the environment and are also deliberately Chemical contaminants can sometimes be added to some processed foods as a pre- introduced as a result of food processing servative and colour fixative. They are, and storage. Drinking water can be for example, particularly important for contaminated from lead used in water controlling the growth of Clostridium storage tanks and piping and this has on botulinum in cured meats. Under suitable occasion caused cases of lead poisoning conditions, the presence of nitrate/nitrite in children (9). Lead-based solder used can lead to the formation of nitrosamines in certain types of can is the major source which are known to cause cancer in of lead in canned foods, and processors mammals. Studies have shown that food in many countries have now adopted preparation techniques such as malting non-soldered cans as a simple remedy for grain, smoking, drying and broiling of this problem. Lead can also leach into meat and fish and the frying of cured

22 Basic Food Safety for Health Workers meats can, under certain conditions, Konzo is a tropical myelopathy, charac- promote the formation of nitrosamines. terized by the onset of spastic parapare- sis, which occurs as epidemics in rural To reduce exposure to these compounds, areas of Africa as a result of consuming good manufacturing practices are insufficiently processed cassava. It can recommended which include addition to arise when rapidly growing populations foods of the minimum amounts of experience declining agricultural yields nitrates/nitrites necessary to achieve and resort to cultivating high-yielding their functional purpose and the use of bitter cassava with high cyanogen levels, nitrosation inhibitors such as ascorbate. though other factors have also been shown to contribute. For example, in the Natural toxicants Bandundu region of the Democratic Re- in foods public of Congo, construction of a new road improved transport to the capital and Many plants that serve as staple human made cassava an important cash crop. To foods often contain a range of secondary meet the higher demand, the women who compounds that are produced to deter were processing cassava reduced the soak- predators (Table 1.3). Over the years, ing time from three days to one, resulting selective plant breeding has to some in higher cyanogen levels in the product. extent reduced the level of these This led to outbreaks of konzo in the dry protective factors, though this of course season when the diet tends to lack sup- increases the plant’s vulnerability to pests plementary foods containing sulfur-amino and disease. Human ingenuity has also acids which are essential for cyanide de- developed processing procedures that toxification. Villages where the traditional eliminate or at least reduce the hazard. three days soaking was retained did not Cooking of legumes, for example, can be report any konzo cases (11). important in destroying protease inhibitors and haemagglutinins (lectins) Glucosinolates are sulfur-containing which, if ingested, can inhibit growth and compounds produced from amino acids. sometimes cause illness. They occur particularly in cruciferous plants such as mustard, cabbage, Failure to recognize the significance of broccoli, turnip and water cress where certain traditional food processing they contribute a pungency to the procedures can also lead to food safety product’s flavour. Cooking can reduce problems. One good example of this is levels by up to 60%. In some cases, cassava which serves as the major source glucosinolates have been associated with of dietary energy for about 500 million hypothyroidism, endemic goitre, but people worldwide. All cassava cultivars problems with their toxicity appear to contain the cyanogenic glucosides, have been mostly associated with the linamarin and lotaustralin. When the growth impairment of farm animals. In plant tissues are damaged, these com- contrast, a number of epidemiological pounds are attacked by the enzyme studies have indicated that consumption linamarase which degrades them to of cruciferous vegetables is associated cyanohydrins which then decompose to with a lower risk of tumour formation in release hydrogen cyanide. Processing of the human digestive tract, suggesting that cassava which involves extended they exert a protective effect against crushing and soaking of the roots carcinogenesis (12). maximizes conversion of the bound cyanide to its free form which is much Favism is an acute haemolytic reaction easier to remove. found primarily around the Mediterranean

23 Foodborne hazards

1 3 2

Biological Factors Harvesting Factors Environmental Factors s Susceptible Crop+Compatible s Temperature Crop Maturity Toxigenic Fungus Moisture Temperature Mechanical Injury Moisture Insect/Bird Damage Detection/Diversion Fungus

Storage Temperature s Moisture Detection/Diversion

Distribution-Processing Detection/Diversion s

Humanss Animals s Animal products Mycotoxins in human nutrition and health 1994, adapted from J.E.Smith, G.L.Solomons, C.W.Lewis & J.G. Anderson, European Commission DGXII Figure 2.4 Factors influencing the production of mycotoxins in foods

and in the Middle East in people with an cholinesterase and has been implicated inherited deficiency of the enzyme glu- in cases of human illness where the cose-6-phosphate dehydrogenase. It is symptoms involve gastrointestinal upset triggered by exposure to fava beans (Vicia and neurological disorders. fava) and is thought to be caused by alkaloids such as vicine which occur in the Biological sources skin of the bean. Lathyrism, a condition characterized by a Mycotoxins spastic paralysis of the legs, is associated with consumption of the pulse Lathyrus Some moulds have the ability to produce sativus in North Africa and Asia. It is toxic metabolites, known as mycotoxins, caused by a neurotoxin which can be which can produce a range of disorders removed from the pulse by prolonged from gastroenteritis to cancer. More than boiling in water. Its toxicity is well known 300 mycotoxins have been identified but but the plant is hardy and survives adverse only a relatively small number have been conditions well. Outbreaks of illness are shown to occur in foods and feeds at lev- particularly associated with times of els sufficient to cause concern. A list of severe food scarcity when it can form a these and some of their characteristics is major part of the diet. presented as Table 2.1. Solanine is a glycoalkaloid found in The aflatoxins are probably the most ex- potatoes. Concentrations are highest in tensively studied mycotoxins. They were the sprouts and skin (especially when discovered in the United Kingdom in the green) and it is not destroyed by cooking. early 1960s following the death of thou- It is an inhibitor of the enzyme sands of turkey poults which had con-

24 Basic Food Safety for Health Workers

Table 2.1 Toxicity and biological effects of some major mycotoxins found in foods

-1 Mycotoxin Major Foods Common producing spp. Biological activity LD50(mg kg ) Aflatoxins Maize, groundnuts, figs, tree nuts Aspergillus flavus Hepatotoxic,carcinogenic 0.5 (dog),

(Aflatoxin M 1 (secreted by cow after Aspergillus parasiticus 9.0 (mouse)

metabolism of Afl B1) Milk, milk products)

Cyclopiazonic Cheese, maize, groundnuts, Aspergillus flavus Convulsions 36 (rat) acid Rodo millet Penicillium aurantiogriseum

Deoxynivalenol Cereals Fusarium graminearum Vomiting, feed refusal 70 (mouse) Fusarium culmorum

T-2 toxin Cereals Fusarium sporotrichioides Alimentary toxic aleukia 4 (rat)

Ergotamine Rye Claviceps purpurea Neurotoxin -

Fumonisin Maize Fusarium moniliforme Equine encephalomalacia pulmonary oedema in pigs oesophageal carcinoma ?

Ochratoxin Maize, cereals, coffee beans Penicillium verrucosum Nephrotoxic 20–30 (rat) Aspergillus ochraceus

Patulin Apple juice, damaged pomme fruits Penicillium expansum Oedema, haemorrhage possibly carcinogenic 35 (mouse)

Penitrem A Walnuts Penicillium aurantiogriseum Tremorgen 1.05 (mouse)

Sterigmatocystin Cereals, coffee beans, cheese Aspergillus versicolor Hepatotoxic, carcinogenic 166 (rat)

Tenuazonic acid Tomato paste Alternaria tenuis Convulsions, 81 (female mouse) haemorrhage 186 (male mouse)

Zearalenone Maize, barley, wheat Fusarium graminearum Oestrogenic not acutely toxic sumed feed containing groundnut meal For example, the risk of liver cancer is contaminated by the mould Aspergillus believed to increase with the prevalence flavus. Since the fungi producing of hepatitis B in the population (13). aflatoxins are prevalent in areas of high The FAO has estimated that up to 25% humidity and temperature, crops in tropi- of the world’s foods are significantly cal and subtropical regions are more sub- contaminated with mycotoxins (14). ject to contamination. They are produced by moulds infecting Aflatoxins are acutely toxic and have agricultural crops, particularly cereals and been shown to be carcinogenic for some oilseeds, during both growth and post- animals. Their toxicity varies between harvest storage and their occurrence is different species but data from a large the result of complex interactions outbreak of poisoning in India in 1974, between the toxinogenic organism, the which involved mouldy maize and in host plant and a range of environmental which nearly 100 people died, suggests factors (Figure 2.4). Mycotoxins can also that the toxicity of aflatoxin B1 for occur in milk, meat and their products as humans lies somewhere between that for a result of animals consuming mycotoxin- the dog and that for the rat. The involve- contaminated feed. Aflatoxin M1 is a ment of aflatoxins with human cancer is metabolite of aflatoxin B1 which is itself more complex and remains to be defined. thought to be carcinogenic and can be

25 Foodborne hazards

isolated from a cow’s milk 12 hours after Algal toxins consumption of the aflatoxin B1. It is A number of algae can produce heat-re- unaffected by pasteurization treatments sistant toxins which are not destroyed and will persist into products such as when the alga is eaten by a predator. The yoghurt, cheese and cream. It can also toxin can then be passed up the food be isolated from human breast milk. chain and accumulated by other However, it is thought to be consider- organisms which are eaten by people. ably less potent than aflatoxin B1. Ciguatera poisoning, a sometimes fatal Mycotoxins differ in their chemical and condition characterized by nausea, physical properties but most can be con- vomiting, diarrhoea and sometimes sidered relatively stable to heat and other neurosensory disturbances, convulsions processes normally applied in the produc- and paralysis, is the most common tion and preparation of food. A number example with thousands of cases of countries have established limits for occurring each year in tropical and mycotoxins in particularly susceptible subtropical regions. Details of the foods (Table 2.2). etiology of ciguetera poisoning are described in Chapter 3. Transmission of algal toxins to humans is often associated with the consumption

Table 2.2a The range of regulatory limits for mycotoxins

Mycotoxin Reg. Limit (µg kg-1) Number of Countries Aflatoxins in foods 0* 48

Aflatoxin M1 in milk 0*–1 17 Deoxynivalenol in wheat 1000–4000 5 Ochratoxin A in foods 1–300 6 Patulin in apple juice 20–50 10 T-2 Toxin 100 2 Zearalenone 30–1000 4 * Limit of determination

Table 2.2b Maximum acceptable levels for aflatoxin for a selection of countries (Aflatoxin B, unless otherwise stated)

Country Limit (µg kg-1) Foods

United Kingdom 2 Nuts, dried figs and their products 5 As above but intended for further processing United States 20 Total aflatoxins in all foods

0.5 Aflatoxins M1 in whole milk, low fat milk and skim milk Australia 5 All foods except peanut products 15 Peanut products India 30 All foods Japan 10 All foods China 50 Rice, peanuts, maize, sorghum, beans, wheat, barley, oats

26 Basic Food Safety for Health Workers

Table 2.3 Principal algal intoxications associated with shellfish

Syndrome Symptoms Toxin Algal species Amnesic choking, vomiting, domoic acid Pseudonitzschia shellfish poisoning diarrhoea, pungens incapacitating headaches, seizure and short-term memory loss Diarrhetic diarrhoea, vomiting, okadaic acid Dynophysis acuta shellfish poisoning abdominal pain, dinophysistoxin Dynophysis acuminata nausea (may persist for several days) Dynophysis fortii Neurotoxic paresthesia, brevetoxins Ptychodiscus brevis shellfish poisoning reversal of hot and cold temperature (Gymnodium breve) sensitivity myalgia and vertigo (generally mild) Paralytic tingling, numbness in fingertips saxitoxin Alexandrium (Gonyaulax) shellfish poisoning and lips, giddiness, staggering, gonyautoxin catenella incoherent speech, Alexandrium tamarensis respiratory paralysis (high mortality rate) of shellfish. More widespread than even greater damage if swallowed. For ciguatera intoxication, cases have been this reason, food manufacturers take reported from locations all over the world. great care to reduce the risk of this hap- Four distinct syndromes are recognized pening by restricting the use of glass in and some of their features are described equipment and sheathing light fittings to in Table 2.3. prevent glass dropping into food in the For sufficient toxin to accumulate it is event of a bulb or tube breaking. Often, usually necessary for there to be a sud- of course, glass is the packing material den increase or bloom of toxigenic algal of choice for foods and great care must species in a locality. This is usually a re- be taken to avoid breakage or damage to sult of a combination of climatic condi- containers that could result in slivers of tions, light, salinity and nutrient supply glass being packed with the food. Sharp and when it occurs the only preventive stones, pieces of metal, bone or wood measure is to ban the harvesting and con- can cause similar problems. sumption of shellfish from these areas. Any hard object can damage teeth and an even wider range of other, often ap- parently innocuous, objects can cause Physical hazards choking when swallowed. These often pose a particular risk for young children. At almost any stage in its production, To minimize such risks, commercial food food can be contaminated with foreign manufacturers go to great lengths, install- material that could be a physical hazard ing devices such as metal detectors and to the consumer. Physical hazards are X-ray machines to detect foreign objects very diverse and difficult to categorize in food, and controlling the quality of since it is possible to conceive circum- their raw materials and the production stances in which almost any foreign ob- environment. Such measures are inap- ject could cause harm. Some, such as propriate to domestic food preparation pieces of glass, pose an obvious risk of where care and vigilance are the best cutting the consumer’s mouth or doing ways to avoid physical hazards.

27 Foodborne hazards

KEY POINTS

l Foodborne hazards can be classified as biological, chemical or physical.

l Biological hazards can be posed by parasites, viruses or bacteria.

l Chemical contaminants in foods can come from industrial and agricultural sources, from food processing or from the food itself.

l Toxic chemicals also come from biological sources such as moulds and algae.

l Foreign objects present in food could constitute a physical hazard to the consumer.

28 Basic Food Safety for Health Workers

Chapter 3 Factors leading to microbial foodborne illness

Three key factors generally contribute to places that are far too inhospitable for outbreaks of microbial foodborne illness: higher life forms, such as in hot sulfur springs. As a result, foods are hardly ever n contamination - pathogens must be present in the food; sterile, that is to say completely free from viable microorganisms. Foods carry a n growth - in some cases they must also mixed population of microorganisms have the opportunity to multiply in the derived from the natural microflora of food in order to produce an infectious the original plant or animal, those picked dose or sufficient toxin to cause ill- up from its environment and those ness; introduced during harvest/slaughter and n survival - when present at a danger- subsequent handling, processing and ous level they must be able to survive storage. in the food during its storage and Most of the microorganisms in our processing. environment cause us no harm. In fact they play very useful roles in making soil fertile and decomposing and recycling Contamination: how organic and inorganic materials that would otherwise accumulate. When they do microorganisms occur in foods, many of these organisms have no evident effect on the food or the get into food? person consuming it. In some cases, microorganisms may actually produce Microorganisms, particularly bacteria, can beneficial changes in the food and this is be found almost everywhere. They are the basis of the large range of fermented present in the air, water and soil; they can foods such as cheese, yoghurt and grow wherever higher organisms can fermented meats. Others, however, will grow, and can be found on the surfaces spoil the product making it unfit for of plants and animals as well as in the consumption and some can be harmful mouth, nose and intestines of animals, to humans causing illness when they or including humans. They also occur in the toxins they produce are ingested.

29 Factors leading to microbial foodborne illness

It is possible to control and minimize the In most cases the animal or bird will carry numbers of organisms present in food by these organisms without showing signs of using good hygienic practices in its ill-health, and pathological lesions will not preparation and handling or by process- be visible during meat inspection. Oth- ing the food in some way. If pathogens ers, such as Bacillus anthracis, the causa- all came from the same source then the tive agent of anthrax, can cause an ill- task of controlling them would be much ness in the animal and visible lesions. simpler. Unfortunately they can get into Since this and other animal diseases can foods from several different sources (Fig- be transmitted to humans, it is clear that ure 3.1), known as reservoirs of infec- meat from obviously sick animals must tion, and by a number of routes. not be used as human food. Other diseases, such as bovine tuberculosis, bru- Microorganisms that occur cellosis or the presence of parasites such as the beef and pork tapeworms and the naturally in foods (indigenous roundworm Trichinella spiralis, may also microflora) be diagnosed during post mortem meat inspection. Thus ante and post mortem Food materials, plant and animal, will examination by a trained inspector is an carry their own microflora during life and essential protection measure. this can persist into the food product. In terms of food safety, the natural microflora is of greatest importance in Natural inhabitants animal products. The muscle of healthy animals and poultry is usually almost of the environment completely free from microorganisms but Many pathogens can be found as natural the intestines in particular carry a very inhabitants of the environment — the large and diverse microflora that can in- soil, air and water where the food is pro- clude human pathogens such as duced — and can, as a result, contami- Campylobacter, Salmonella and certain nate the product. For example, Vibrio strains of Escherichia coli. In the process parahaemolyticus is a naturally occurring of slaughter and butchering a carcass, marine organism in warm coastal waters these organisms may be spread to other and can contaminate fish. Some strains meat surfaces. As a result, evisceration are pathogenic and this can be a very im- and dressing are regarded as key steps portant cause of foodborne illness where that need to be hygienically performed fish is a major item in the diet. Clostrid- to minimize meat contamination. ium botulinum and Clostridium perfringens are

Food handlers

(e.g. soiled hands) Flies &

é pests Polluted water Human & animal é (e.g- wastewater,

excreta é irrigation and

Food household water) Infected food animals (Raw/Cooked) é é Dirty pots &

cooking utensils Indigenous é é

microflora é Cross.contamination Domestic animals during food preparation

Figure 3.1 Sources of food contamination

30 Basic Food Safety for Health Workers found in soil and mud. Bacillus cereus Filter-feeding shellfish will filter large spores can be isolated from soil and air, volumes of water to extract nutrients. If and Listeria monocytogenes is a relatively this water is polluted with sewage they common environmental organism found will also concentrate pathogenic bacteria in unpolluted water, mud and numerous and viruses in their tissues. Polluted water other sources. used in aquaculture can also lead to the carriage of pathogens such as Vibrio cholerae by farmed fish and shellfish. Polluted environment: Animal excrement poses equally serious insanitary practices in problems. For example, a large outbreak agriculture and aquaculture of listeriosis was caused by the contamination of cabbages with sheep manure. Pollution of the environment with ani- Chicken faeces adhering to the outside mal or human wastes such as sewage can of egg shells can contaminate the con- be a serious threat to food safety. Hu- tents when the egg is broken and this has man excrement can contain a wide range been the cause of numerous outbreaks of pathogens transmitted by the faecal- of salmonellosis. Sometimes the link be- oral route including bacteria such as Vi- tween the food and faecal contamination brio cholerae, Salmonella Typhi, viruses such can be quite complex, as was illustrated as Hepatitis A, and parasites. These can by an outbreak of yersiniosis (Figure be transferred to foods if raw sewage is 3.2). In this case, crates used to trans- used to fertilize fields or if the water used port waste milk to a farm where it was to irrigate, wash, cool or transport food used as animal feed were contaminated is contaminated with sewage. with pig excrement. Back at the dairy, the

Figure 3.2 Faecal contamination leading to an outbreak of yersiniosis

31 Factors leading to microbial foodborne illness

crates were insufficiently washed and dis- though chemical contaminants can also infected before being used to transport be a problem, since more than half of retail milk to the shops. During this proc- the world’s population is still exposed to ess the outside of the milk cartons were water contaminated with pathogens. contaminated with Yersinia enterocolitica which was, in turn, transferred to the milk Pests and pets when the cartons were opened and the milk poured. It is not just food animals that frequently carry pathogenic organisms in their Water gastrointestinal tract. Surveys have shown that up to 15% of pet dogs ex- Contaminated water is simply one aspect crete salmonellae. Rats and mice can of a polluted environment, but in view transmit illness by contaminating food of its importance in foods and food with organisms picked up from sewers, processing and its role as a major source garbage and other sources via their fur, of diarrhoeal disease in developing coun- urine, faeces or saliva. tries it merits special mention. Contami- nation of water with faeces can introduce Wild birds can often find their way into a wide variety of pathogenic bacteria, food processing areas, particularly in hot viruses, protozoa and helminths which climates where buildings are relatively can be transmitted to people when the open, and these may excrete pathogens water is used for drinking or in food such as Salmonella and Campylobacter. preparation. Since individual water Flies, cockroaches, ants and other insect sources tend to serve large numbers of pests can transfer organisms from sources people, disease outbreaks where water is contaminated with pathogens to foods. the primary source of infection can be Flies are particularly important in this very large. This linkage between water respect as they are associated with both and the spread of disease has been food handling areas and contaminated known for a long time and is reputed to areas such as toilets and refuse heaps. have been dramatically demonstrated in They also have the unfortunate habit of 1854 by John Snow when he removed feeding by regurgitating their previous the handle from a water pump in Broad meals on to foods to help liquefy them. Street, London, to bring a local cholera outbreak to an end. Spiders and wasps are rather less of a hazard because they tend not to breed in Although pathogen-contaminated water contaminated areas but nonetheless they is clearly a prime source of infection, it have the potential to transfer pathogens is also true that a simple insufficiency of to food. water will hamper efforts to practise good personal and food hygiene and contrib- The food handler ute to the transmission of disease. Handling of food can introduce and Recognition of the pressing need to pro- spread pathogenic microorganisms. Food vide safe drinking water led to the pe- handlers may carry pathogens without riod 1981–1990 being declared the In- experiencing any serious ill-effects them- ternational Drinking Water Supply and selves. Staphylococcus aureus is commonly Sanitation Decade. This resulted in the associated with the skin, nose, throat and WHO Guidelines for Drinking Water infected skin lesions, particularly in higher Quality. These guidelines place their pri- primates such as humans where 20–50% mary emphasis on microbiological safety, of healthy individuals can carry the or-

32 Basic Food Safety for Health Workers ganism. The organism is difficult to re- food handler who was also a chronic move from the skin where it “hides” in carrier of the illness. In the early years of pores and hair follicles. If the hands are the 20th century the unfortunate combi- damp it can be drawn to the surface and nation of her medical condition and her transferred to foods. It is possible to iden- chosen profession, a cook, is estimated tify carriers by microbiological testing and to have resulted in about 1300 cases of this has been done on a number of occa- typhoid fever in the USA. Infected food sions. In one recent example, restaurant handlers are also a common source of workers in Kuwait city were tested and foodborne viruses such as the Hepatitis in a sample of 500 people 26.6% were A virus and the diarrhoea-causing, small found to carry the organism (15). It is not round-structured viruses which are ex- usually feasible to do this routinely to creted in large numbers (108-1010 g-1 fae- identify Staphylococcus aureus carriers so, as ces) by infected individuals. Many cases a general precautionary measure, people of foodborne virus infection have been should avoid handling foods with bare associated with catering. hands as much as possible, particularly those foods that support the growth of Equipment, utensils and S. aureus. kitchen practices Organisms that reside in the gut can be transferred to food if food handlers fail The equipment and utensils used in the to wash their hands thoroughly after us- preparation of food can also act as ing the toilet. Gut organisms adhere less sources of contamination. For instance, strongly to the skin and should be read- knives or chopping boards used with un- ily removed by washing with soap and cooked products such as raw meat or water. Thorough hand-washing is essen- poultry can become contaminated with tial after using the toilet, not just after pathogens. If they are used again with- defecation, since pathogens can also be out being adequately cleaned, particularly picked up from previous users of the toi- if they are then used with a cooked or let via door handles, taps and drying tow- ready-to-eat product, the pathogens can els. be transferred, posing a very serious threat to food safety. This can also hap- The risk is very much greater if the food pen if food handlers who work with raw handler is suffering from a gut infection. food fail to wash their hands before han- In many cases, however, infected food dling ready-to-eat food. This process, handlers may not know that they are car- whether mediated by hands or equip- rying the pathogen in their gut as they ment, is known as cross-contamination. may not feel unwell and may exhibit no Raw foods can also contaminate cooked symptoms. This could be because they or ready-to-eat foods if they are stored are in what is known as an acute carrier together improperly. For example, if raw state where they are infected, can spread meat is stored above cooked foods in a the organism, but have not yet begun to refrigerator, liquid drip from the meat can display symptoms. Alternatively, they contaminate the foods stored below. may be chronic carriers who are infected but will not develop symptoms, yet will Dishcloths left wet can also act as an excrete the pathogen over a long period. important reservoir of contaminating This latter state has been most famously organisms that can be spread around associated with typhoid fever, particularly foods and food contact surfaces as the the notorious case of “Typhoid Mary”, a cloth is used.

33 Factors leading to microbial foodborne illness

low levels to numbers well in excess of Growth the infectious doses quoted in Table 1.6. In eight hours a single organism with a We have already noted that an important generation time of 20 minutes can reach feature of the transmission of foodborne a population of more than 16 million illness is that bacterial pathogens can (Figure 3.3). The ability of bacterial grow in some foods. In a relatively short pathogens to multiply in foods explains period, they can multiply from a low, why, in some circumstances, foods can possibly harmless level to numbers suf- be more likely to provide the minimum ficient to cause illness. This does not hap- infective dose of a pathogen than con- pen with other foodborne pathogens such taminated water. as parasites and viruses and it is there- Moulds and yeasts also have the capac- fore important to understand the factors ity to grow in foods but, with the notable that influence whether and how quickly exception of mycotoxin production by bacteria can grow in food. some moulds, this normally results in Bacteria multiply by a process of dou- spoilage rather than health problems. bling; each cell splits into two identical Moulds and yeasts grow by different daughter cells which go on to repeat the mechanisms than bacteria: most yeasts process, giving four cells, which then pro- tend to multiply by budding to produce a duce eight cells, and so on. The period daughter cell which separates from its between cell divisions is known as the parent, while moulds tend to grow as fine generation or doubling time. This can be thread-like structures called hyphae quite short, typically around 20 minutes which extend and branch to produce a or so, and sometimes even shorter. A fig- tangled mass known as a mycelium. ure of just over seven minutes at 41oC For microorganisms to grow at their fast- has been reported for the pathogen est, conditions have to be just right. Op- Clostridium perfringens. This means that, timum growth conditions differ slightly given the right conditions, a bacterium for bacteria, yeasts and moulds and this can multiply very rapidly from extremely can determine the type of organism that

>16 million

One bacterial cell

Figure 3.3 Exponential growth of bacteria

34 Basic Food Safety for Health Workers predominates when foods spoil. Moulds ply of nutrients will be limited and it will and yeasts generally grow more slowly grow only slowly or perhaps not at all. If, than bacteria and are often outgrown by however, the pathogen is introduced after them unless conditions in the food are the food has been cooked and the natural sufficiently inhibitory to bacterial growth microflora has been eliminated or to give the moulds and yeast a competi- severely reduced there will be little or no tive advantage. The most important of competition for growth and the patho- the factors that affect microbial growth gens will grow more quickly. are: Pathogen growth is much less likely to n availability of nutrients occur in water where the nutrient supply n temperature is more limited. n acidity/pH n available water (water activity, aw) Temperature n oxygen (air) n antimicrobial agents. Microorganisms can be found growing at o n time. temperatures ranging from about -10 C up to more than 100oC. The most Availability of nutrients important consideration is that water should be present in its liquid state. If it When microorganisms grow on foods, is present either entirely in the solid state, they use them exactly as we do — as a as ice, or as water vapour, then bacteria source of nutrients and energy. Foods cannot grow even if they can cope with generally contain a variety of chemicals the extreme temperature under those that serve these purposes very well and conditions. levels of nutrients are not usually limiting Individual microorganisms will not grow factors on microbial growth in foods. over such a wide temperature span and This means that food handling equipment are normally restricted to a range of about must be very thoroughly cleaned after use 35oC. They have a minimum to remove all traces of food since bacte- temperature below which they cannot ria will grow on the tiniest remnant and grow, a maximum temperature above this can contaminate subsequent batches. which they cannot grow and in-between A raw food will contain a diverse micro- an optimum at which they grow best. bial population with many different or- These three temperatures, known as an ganisms competing for the nutrients organism’s cardinal temperatures, are available. If a pathogen is present it may used to separate microorganisms into dif- not do well in this competition; its sup- ferent classes (Table 3.1).

Table 3.1 Cardinal temperatures for microbial growth Temperature (°C) Group Minimum Optimum Maximum Thermophiles 40–45 55–75 60–90 Mesophiles 5–15 30–45 35–47 Psychrophiles (obligate psychrophiles) -5–+5 12–15 15–20 Psychrotrophs (facultative psychrophiles) -5–+5 25–30 30–35 Adapted from ICMSF, Microbial Ecology of Foods Volume 1, New York Academic Press 1980

35 Factors leading to microbial foodborne illness

Most foodborne pathogens are No pathogenic bacteria will grow at tem- mesophiles with an optimum growth peratures above about 60oC and this de- temperature around body temperature of fines the upper limit of a “danger zone” 37oC. This makes sense since for many of temperature ranging from below 10oC of them the preferred habitat is the to 60oC. Foods that are ready to serve human or animal body. In tropical should not be stored at temperatures in developing countries foods may be stored this range as there is the potential for at temperatures as high as 37oC. bacterial growth to occur. Mesophiles will grow rapidly at this temperature, though they can also grow quite Acidity/pH well down to below 20oC. Their minimum growth temperature is generally Acidity and alkalinity are measured by around 8oC, so if a food is stored below pH, a number which reflects the concen- 10°C then mesophiles will either grow tration of hydrogen ions present. Pure very slowly or not at all (although they water is taken as neutral with a pH of 7. may survive, see Figure 3.4 and below). Below a pH of 7 the concentration of hydrogen ions is higher and conditions Because of the great use of refrigeration are said to be acidic; above 7, the in modern food processing, handling and concentration of hydrogen ions decreases distribution, there has been a lot of con- and conditions are described as alkaline. cern about pathogens that are capable of growing at chill temperatures (<8oC). As with temperature, microorganisms These are the psychrotrophic pathogens will grow over a restricted range of pH (Table 3.2). Although these organisms and have a smaller pH range over which are capable of growing in refrigerated they grow fastest. For most bacteria the foods, they grow very slowly. Their gen- optimum pH is around neutrality (pH 7); eration time at 4–5oC is normally 10–25 yeasts and moulds generally have an op- hours. timum more on the acid side (below 7). Table 3.2 Psychrotrophic foodborne pathogens Aeromonas hydrophila Clostridium botulinum (non-proteolytic) Listeria monocytogenes Yersinia enterocolitica

Freezing of foods starts at temperatures just below 0oC but is not complete until much lower temperatures are reached. Very few microorganisms will grow at temperatures below 0oC and none will grow in properly frozen foods (<-18oC) although, like microorganisms in chilled foods, they may survive and can resume growth if the temperature increases (Fig- ure 3.4). Parasites such as protozoa, cestodes, trematodes and nematodes are much more sensitive to freezing and die during frozen storage. Figure 3.4 Effect of temperature on bacterial growth

36 Basic Food Safety for Health Workers

Most foods are slightly acid although where much of the water may be “occu- some, such as citrus fruits, pickles and pied” with keeping the salt or sugar in sauces, are much more acidic. Pathogens solution, or in frozen foods where the cannot grow in the more acidic foods but water is present as ice. are relatively unaffected by the pH found in most food materials. Acids differ in Water availability is often measured or expressed in terms of water activity (a ). their ability to prevent microbial growth; w acetic (ethanoic) acid is generally more This is a scale from 0 to 1; pure water with maximum water availability has an a of effective than lactic acid which in turn is w more effective than citric acid. Usually 1, in the complete absence of water the a would be 0. Dried milk powder has a if a food has a pH below 4.5 it is w considered safe from bacterial pathogens. water activity of 0.2. Bacteria normally Despite this, there have been occasional require a very high water availability to be well-documented outbreaks of foodborne able to grow at their fastest, but will often illness associated with acidic foods such be able to grow somewhat more slowly in as yoghurt. salty or partially dried foods. Salmonella will grow in the presence of 6% salt, Listeria monocytogenes in 10% salt, and some strains Water activity (aw) of Staphylococcus aureus in 20% salt. To be All microorganisms require liquid water certain that pathogen growth is prevented, to enable them to grow. If there is little it is necessary to dry foods down to very water present, or the water that is present low moisture content or add very high is not available to the microbe, then its levels of salt or sugar (Figure 3.5). Total growth is slowed or even prevented. It inhibition of growth, however, is not may be the case that there is simply not always necessary; Staph. aureus is the enough water present, as in some dried pathogen that is most tolerant of low water foods. Alternatively, water may be availability and will grow down to an aw present but unavailable, as in foods that of 0.83 but it will not produce toxin if the contain high levels of salt or sugar and aw is 0.86 or below.

Water Activity(aw) Food Microorganisms & minimum aw for growth

High moisture 1.00–0.98 Meat, fruit, milk, vegetables

0.98–0.95 Yogurt, evaporated milk, tomato paste 0.95–0.94 Clostridium botulinum 0.93 Baked goods Salmonella 0.90 Most bacteria 0.90 0.88–0.85 Jam, old cheese Most yeasts, Staphylococus aureus 0.80 0.80 0.75 Figs, dried dates, molasses Most moulds, halophilic 0.70 bacteria (salt loving) 0.70 Parmesan cheese, dried fruits Osmophilic yeasts, 0.61 xerophilic moulds 0.60 Chocolate confectionary, 0.50 honey, cocoa 0.40 Potato flakes, crisps 0.30 Crackers, cake mix Dry 0.20 Dried milk, dried vegetables Figure 3.5 Water activity, foods and microbial growth

37 Factors leading to microbial foodborne illness

As aw is decreased, bacteria are inhibited anaerobes and positively require oxygen- first (Figure 3.5), followed by moulds and free conditions. yeasts. Some organisms are particularly Antimicrobial agents adapted to growing at low aw values — such as the halophilic bacteria, and some Foods were all once living organisms moulds and yeasts — but these are which possessed systems to protect them associated mainly with spoilage from microbial infections that might problems. No microbial growth at all damage them. Some of these systems can occurs when the a is below 0.6. w persist into the food product and help

The aw of a food is also related to the inhibit microbial growth. They are mainly relative humidity of its storage associated with plant foods, though there environment. If a food is stored in a are a number of antimicrobial systems in closed container and allowed to foods such as eggs and milk that equilibrate with the atmosphere that contribute to their stability. Some surrounds it, the relative humidity of the antimicrobial plant components such as

atmosphere will become equal to the aw benzoic acid have also been deliberately of the food. Thus, for example, dried added to foods as preservatives.

fruit with an aw of 0.72 would be in Generally their effect is limited and equilibrium with an atmospheric relative should not be overestimated. Garlic when humidity of 72% (0.72 of saturation). crushed produces the antimicrobial This has important implications for the component, allicin, but crushed garlic in storage of dried foods where, if the oil has nevertheless been the cause of a relative humidity of the environment is botulism outbreak (16).

higher than the aw, water will condense on the food. This will increase the food’s Antimicrobials are added to foods principally to inhibit spoilage organisms. aw, perhaps bringing it into a range where mould growth can occur. One notable exception to this is the artificial preservative nitrite which is of Oxygen (air) major importance in cured meats as an inhibitor of Clostridium botulinum. Air comprises about 20% oxygen. Most Outbreaks of botulism caused by cured microorganisms grow much faster if meats are often the result of failures in oxygen is present at this concentration and the curing process which have resulted are known as aerobes. Some, such as in insufficient nitrite being present. moulds, are obligate aerobes which means that they cannot grow at all if air (oxygen) Time is absent. However, for some bacteria — the obligate anaerobes — the presence of The final, and in many ways the most oxygen is actually toxic. Restricting the important factor of all, is time. Bacteria presence of oxygen and increasing the level can grow to dangerous levels if they have of other gases such as carbon dioxide is a the right conditions for growth, but only useful way of preserving some foods since if they have sufficient time to do so. many of the normal spoilage organisms Microorganisms will grow fastest in foods will not grow under these conditions. with no inhibitory factors and these Pathogenic bacteria, however, are largely therefore have the shortest safe shelf-life. unaffected. Most are what are known as However, a food may have a water facultative anaerobes which can grow in availability and pH that slows the growth the presence or absence of air, and some, of a pathogen but this will be of little such as Clostridium botulinum and help if the food is left for long periods Clostridium perfringens, are obligate allowing sufficient growth to occur.

38 Basic Food Safety for Health Workers

A (D=1/2min)

B (D=1min)

0 minutes 1 minute 2 minutes

Heating time u

Figure 3.6 Effect of heat resistance (D value) and initial numbers on the survival of bacteria during heating

numbers sufficient to cause illness. Even Survival where the numbers are low, the bacteria present can resume growth and multiply It is also important not to forget the pos- very rapidly to high levels if conditions sibility of microbial survival. If bacteria are changed. This could happen if, for ex- are present in sufficient numbers in a food, ample, a dehydrated product is mixed it may not be necessary for them to grow with water and left to stand, or a frozen in it to produce illness; all they have to food is left too long defrosting at tem- do is survive to maintain those numbers. peratures suitable for pathogen growth. This is well illustrated by the bacterial pathogen Campylobacter jejuni which does Some adverse conditions do affect both not normally grow in foods but has a low microbial growth and survival. If the pH infectious dose and can survive to cause is too low for a microorganism to grow, it illness. Viruses will multiply only in the will die slowly during storage. It may, cells of the infected individual but can however, take some time for the food to survive in, and be transmitted by, foods. become safe. Little is currently known about the survival of non-bacterial The question of bacterial survival is par- pathogens such as viruses and parasites ticularly important since, in many cases, at the pH levels normally found in foods. conditions that prevent growth enhance survival. For example, microorganisms The most effective and accessible way cannot grow in dried foods and frozen of killing microorganisms is by heating. foods, but they can survive in these foods Above the maximum temperature which for very long periods with only a slight supports their growth, microorganisms decrease in numbers. Foods which will will die. The rate at which they die will not support microbial growth can still, increase as the temperature increases. The therefore, contain pathogenic bacteria in conventional way in which we describe

39 Factors leading to microbial foodborne illness

Figure 3.7 Factors leading to foodborne illness

this rate is by what is known as a D-value. stability. Foodborne toxins, however, may The D-value for an organism is the time be unaffected by heating. Most that it takes at a particular temperature mycotoxins are stable to normal cooking to kill 90% of a population of that or- procedures, as are some bacterial toxins ganism, i.e. to reduce the number of vi- such as those produced by Staphylococcus able cells by a factor of 10. The smaller aureus and Bacillus cereus. the D-value, the faster the death rate at Some pathogenic bacteria such as Clostrid- that temperature. ium perfringens, Clostridium botulinum and Measured D-values are quite variable and Bacillus cereus produce heat-resistant depend on the type of food material and spores. These will not be killed by con- the particular strain of the organism conventional cooking procedures and could cerned, but for a high moisture product a resume growth after cooking if the food typical bacterial D-value at 65oC can be is stored for too long at an inappropriate 0.1–0.5 minutes (6–30 seconds). If the temperature. temperature is increased by about 5 oC then the death rate will increase about 10-fold. The ability of cooking to solve food safety problems is not therefore unlim- How long a food needs to be heated to ited and wherever possible prevention of make it safe also depends on how many dangerous levels of contamination in the organisms are present initially (Figure 3.6). first place is preferable. High numbers will take longer to kill. To predict accurately how long a food should Foods processed commercially which be heated and at what temperature requires have received a moderate heat treatment quite a detailed knowledge of the food and specifically designed to eliminate non- the pathogens present but, as a general spore forming pathogens and/or spoilage rule, a food should be cooked so that all bacteria are described as being of it reaches at least 70oC. pasteurized. To eliminate sporeforming pathogens and spoilage organisms heat Cooking is not just a useful procedure to processes far in excess of normal cooking, eliminate foodborne bacteria. Foodborne sometimes known as appertization, are viruses and parasites can also be killed, necessary. This is the treatment given to although in these cases we do not have canned foods to ensure that they can be such detailed knowledge of their thermal stored safely for long periods without re-

40 Basic Food Safety for Health Workers

Table 3.3 Factors contributing to outbreaks of foodborne illness England and Wales1 U.S.A.2

Preparation too far in advance 57 29 Storage at ambient temperature 38 63 Inadequate cooling 32 Contaminated processed food 17 n.i. Undercooking 15 5 Contaminated canned food 7 n.i. Inadequate thawing 6 n.i. Cross contamination 6 15 Food consumed raw 6 n.i. Improper warm handling 5 27 Infected food handlers 4 26 Use of left overs 4 7 Extra large quantities prepared 3 n.i.

1. 1320 outbreaks between 1970 and 1982 from Roberts 1985. 2. Outbreaks occurring between 1973 and 1976 from Bryan 1978. n.i. category not included in analysis. frigeration. Further reference to these two Hygienic food handling aims to control processes is made in Chapter 5. the presence of pathogens in foods by Treatment of food with ionizing radia- controlling each of these contributory tion is similar to heat in its effect on mi- factors. When outbreaks of foodborne croorganisms. Non-sporeforming bacte- illness occur it is because there has been ria and parasites will be killed by quite a loss of control over one of these fac- low doses (less than 10 kGy). This can tors. be considered the radiation equivalent of pasteurization and is termed radicidation. WHO data indicate that only a small Bacterial spores and viruses are more re- number of factors related to food han- sistant and require much higher doses to dling are responsible for a large propor- ensure their elimination. Such doses can tion of foodborne disease episodes eve- often produce unacceptable flavour rywhere. Common errors include: changes in the product and are less likely to be used in normal commercial practice. n preparation of food several hours prior to consumption, combined with its Major factors leading to storage at temperatures which favour foodborne illness the growth of pathogenic bacteria or the formation of toxins; We have looked at the three factors that contribute to the presence of dangerous numbers of microorganisms in a food — n insufficient cooking or reheating of contamination, growth, and survival food to reduce or eliminate patho- (Figure 3.7). gens;

41 Factors leading to microbial foodborne illness

n cross-contamination; likely to make more than just one error. n people with poor personal hygiene It may also reflect the fact that to achieve handling the food. an infective dose of a pathogen can require a combination of several errors: There have been several studies of out- initial contamination with the pathogen, breaks of foodborne illness which at- allowing it to multiply, and then failing tempt to identify where the failure has to eliminate it by adequate cooking. The occurred. The results of two such surveys second significant point is that the most are shown in Table 3.3. commonly identified causes are failure to Two points should be apparent from this control temperature and time — failure table. Firstly, the percentages in each to cool foods correctly and store them at column do not add up to 100%. This re- temperatures that prevent microbial flects the fact that in many outbreaks growth, failure to heat them sufficiently several failures of good hygienic practices to kill microorganisms, or prolonged stor- were identified. This is perhaps not so age giving microorganisms time to mul- surprising since, if people are not famil- tiply to dangerous levels. iar with what good practices are, they are

KEY POINTS

l Microorganisms are everywhere.

l Microorganisms can cause illness, they can spoil food, and some can ferment it into desired products.

l Pathogenic microorganisms can be part of a food’s natural microflora, or may be contaminants.

l Contaminants can come from the normal environment, a polluted environment, pests and pets, the food handler and/or equipment.

l Bacteria and moulds are able to grow in foods, increasing the risks that they pose.

l The growth of bacteria and moulds can be extremely rapid.

l This growth is affected by the composition of the food and its storage environment.

l The possibilities of both growth and survival of bacteria must be considered when assessing safety.

l Heating is the most effective single method for improving food safety.

l Ionizing radiation can also help make food safe.

l A number of different factors contribute to outbreaks of foodborne illness, but most include a failure to control temperature/time.

42 Basic Food Safety for Health Workers

Chapter 4 Hazards associated with different foods and their control

Red meat, poultry and their products

Meat can be derived from a huge variety A first step towards ensuring good quality of birds, mammals and reptiles, though meat is, of course, to exclude the use of cattle, sheep, goats, pigs and poultry meat from obviously diseased or sick (chickens, ducks, turkeys) are the animals and to inspect carcasses for signs principal sources. In many countries, of parasitic infections. Good meat is also the product that is most microbiological quality meat, however, often associated with problems of also depends on hygienic slaughter and microbiological food safety. There are two butchering — avoiding the contamina- main reasons for this: tion of freshly exposed meat surfaces from the hide or contents of the gut, ei- n Fresh meat provides bacteria with an ther directly or via the workers’ hands, ideal medium on which they can grow. clothing, equipment or via pests such as It has ample nutrients, available water flies. and a moderate pH. Good hygienic practices in this area can reduce contamination but do not n The animal or bird can also act as the source of pathogenic organisms such necessarily guarantee freedom from as bacteria and parasites found in pathogenic microorganisms. Raw meat meat. It acquires these from its should therefore always be regarded as a environment, feed, water or other likely source of pathogens. This is animals. As outlined in Chapter 3, the supported by statistics from various skin and gastrointestinal tract of the countries. For example, in the United healthy animal carry a large population Kingdom meat or poultry dishes were of microorganisms that can include a incriminated in more than 74% of number of pathogenic bacteria such incidents of foodborne illness. as Escherichia coli, Salmonella and Most meat products are cooked before Campylobacter. These come primarily consumption and this eliminates the veg- from the animal’s gut but can be etative forms of bacteria as well as vi- transferred to the skin via faeces. ruses and parasites. With intact pieces of Parasites, if present, can be found at meat, most of the microorganisms will a number of locations in the animal’s be associated with the meat surfaces and body. will be readily killed by heat. However,

43 Hazards associated with different foods and their control

if the meat has been comminuted, mi- Cooked meats served cold can be particu- croorganisms will be mixed into the bulk larly hazardous. They are susceptible to of the meat making it more hazardous contamination from uncooked products unless thoroughly cooked throughout. which can reintroduce many of the or- Serious recent outbreaks of illness ganisms killed by cooking. They may also caused by E. coli O157 have been linked be subject to environmental contamina- with the failure to cook ground or minced tion with organisms such as Listeria meat products adequately. monocytogenes, and handling can introduce Staphylococcus aureus. Both of these bacte- Cooking is therefore an important meas- ria grow well in meats and can also grow ure for ensuring that food is safe, though readily at the salt levels normally found on its own it is not always sufficient. in cured cooked meats. Contaminants in- Microbial growth before cooking must be troduced into cooked meats even at quite controlled as far as possible to prevent low levels could pose a serious threat since the production of heat stable toxins such they may grow even more rapidly than as those of Staphylococcus aureus. Heat-re- usual as cooking will have reduced sistant bacterial endospores of Clostrid- competition from other bacteria. The ium perfringens and other sporeformers are absence of further cooking also means o resistant to temperatures above 100 C that the viable organisms will persist in and will survive normal cooking. If the the product until it is consumed. meat is not adequately cooled after cooking the spores may germinate, the A number of meat products contain organisms may grow and may rapidly additives such as nitrite and, in some produce large numbers of vegetative countries, sulfur dioxide. Nitrite is cells. If the cooked meat is then eaten particularly important in the control of cold or not adequately reheated before Clostridium botulinum in cured meats such consumption to destroy the vegetative as hams and sausages and failure to cure cells, illness will probably result. Pre- meats sufficiently has resulted in cooked meat dishes such as joints, stews occasional outbreaks of botulism. and casseroles are very common vehicles Because of the distinctive symptoms, for this type of foodborne illness. In some such outbreaks can be traced back cases, however, the meat may not be the hundreds of years. This long association source of the organism. In many of botulism with such meat products is countries it is common practice to add a also reflected in the name of the organism range of spices and herbs to cooked meat which is derived from botulus, the Latin dishes and these may be the source of word for sausage. the Clostridium perfringens spores. For Sulfur dioxide is used in some countries example, one study found a greater as a meat preservative, where its principal incidence of Clostridium perfringens in purpose is to delay spoilage. In doing so foods in Pakistan than in Zambia and it inhibits mainly Gram-negative bacteria this difference was attributed to the which include many important pathogens greater culinary use of spices in Pakistan. such as Salmonella. If spices or herbs are added after cooking As a general rule it is not advisable to eat when the food has cooled slightly, there uncooked meat and this rule is generally is also the opportunity for non- adhered to (popular raw meat dishes such sporeforming pathogens such as as steak tartare being a notable Salmonella or Shigella to survive and grow exception). Many fermented sausages in the product if they are present on the such as salamis are, however, also added ingredient. essentially raw meat products. Most re-

44 Basic Food Safety for Health Workers ceive no heat treatment during their all in a number of foods where they are processing and rely on a combination of used for their functional properties. This antibacterial factors or hurdles for their type of contamination is most likely to keeping quality and safety. They are occur when large numbers of eggs are cured products containing a mixture of broken in commercial food processing salt (sodium chloride) and nitrite, both and, for this reason, bulk liquid egg is of which will inhibit bacterial growth. pasteurized (generally at 64.5oC for 2½ They are also dried to various extents, minutes). It may also occur at household depending on the product, and undergo level, if care is not taken when breaking a fermentation by lactic acid bacteria eggs, and this has been the cause of a which converts sugar to lactic acid, number of outbreaks of salmonellosis. decreasing the pH. If the product is well made, using good quality meat and an efficient starter culture to ensure a rapid Milk and dairy lactic fermentation and pH drop, it is unlikely to pose a problem. In such cases, products the presence of pathogens in the raw material would be very low and those that Milk carefully drawn from the healthy might be present would have little op- animal will have very low levels of portunity to grow and would be likely to bacterial contaminants. However, in die during processing. Failure to observe practice this milk rapidly acquires these rules can, and has, resulted in out- microorganisms from the animal, its breaks of illness caused by Salmonella and immediate environment and from Staphylococcus aureus. equipment. Some of these microorganisms could be pathogens, a number of which are associated with raw milk Eggs and egg products (Table 4.1). Eggs are an animal product with a long association with Salmonella. Normally contamination is located on the outside Table 4.1 Examples of pathogens of the shell as a result of contact with associated with milk the hen’s faeces in the cloaca or in the Mycobacterium bovis nest after laying. The egg shell is normally Brucella spp. an excellent barrier for preventing bacte- Salmonella rial penetration of the egg. Penetration Campylobacter can occur, however, under conditions of high temperature and humidity, and more Listeria monocytogenes commonly with duck eggs than with hens’ E. coli eggs. Some Salmonella serotypes are par- Yersinia enterocolitica ticularly host-adapted and can infect egg Staphylococcus aureus yolk in the oviduct. In hens’ eggs, this Bacillus cereus has been associated in recent years with certain types of Salmonella enteritidis. Salmonella adhering to the outside of the In many countries it is required to heat- shell with faecal material may contami- treat milk before sale to destroy patho- nate the contents once the egg is broken. gens that may be present. Several possi- This can be a problem since eggs are of- ble combinations of temperature and ten lightly cooked and are not cooked at time are often specified in regulations that

45 Hazards associated with different foods and their control

Table 4.2 Examples of time-temperature heat treatment for pasteurization of milk

Low temperature holding (LTH) 63 °C for 30 minutes High temperature short time (HTST) 72 °C for 15 seconds Ultra high temperature (UHT) 135 °C for 1 second “Sterilised” >100 °C typically 20–40 minutes

must be followed carefully (Table 4.2). pasteurization or equivalent heat treat- It is possible to test milk to see if it has ment to assure their safety. Many tradi- been adequately heat-treated. Raw milk tional milk products such as cheeses, contains an enzyme, phosphatase, that is butter and yoghurts, however, evolved inactivated by the prescribed heat treat- before the advent of pasteurization be- ments. In the test, a chemical is added to cause they were safer and more stable a sample of milk which the enzyme, if than raw milk. A number of factors con- present, will convert to a bright yellow tribute to this: yoghurt has a low pH and compound. Failure to observe a yellow hard cheeses combine a reduced pH with colour therefore indicates that the a low moisture content. Butter has a spe- enzyme is not active and that the milk cial physical structure where the water is has been correctly pasteurized. present as many tiny globules spread Where commercially heat-processed milk through a continuous fat phase. Micro- is not widely available, it is both com- organisms in these globules find it diffi- mon practice and a wise precaution to cult to grow because of limited space and boil milk before it is consumed. nutrients and the relatively high local concentration of salt. The antibacterial Heat processing will destroy all but the effect of these factors does not have the heat-resistant spores such as those of same degree of certainty that is associ- Bacillus cereus. B. cereus is a common spoil- ated with heat treatment. Therefore there age organism of heat-treated milks, but is a greater risk of these products caus- milk-associated cases of B. cereus intoxi- ing illness when they are made from raw cation are rare. Heating will also not de- milk since it is more likely to contain stroy the enterotoxin produced by Staphy- pathogens at a level sufficient for some lococcus aureus and outbreaks have been to survive processing. This is reflected caused by dried milk where S. aureus was in Table 4.3 which describes reported allowed to grow and produce enterotoxin outbreaks of foodborne illness due to before drying. cheese since 1980 and shows the prepon- Inadequate pasteurization or environ- derance of cheeses made from raw milk. mental contamination of milk with Sal- monella after pasteurization has also caused problems with dried milk. Under Fish, shellfish and dry conditions, the organism can survive for prolonged periods though it cannot fishery products grow until the milk is rehydrated. Ex- tremely high standards of hygiene are Fish and shellfish can become contami- therefore essential in the processing of nated from their natural environment or milk. from subsequent handling or processing. Most commercial processing of milk into Fish and shellfish act as intermediate products such as cheese, yoghurt, butter hosts for a number of parasites that can and dried milks includes a preliminary infect humans (Table 4.4). Illness caused

46 Basic Food Safety for Health Workers

Table 4.3 Examples of reported outbreaks of foodborne disease due to cheeses Outbreak Pathogen no. of cases no. of deaths Food USA, 1985 L. monocytogenes >142 48 mexican-style cheese* Switzerland, 1983–87 L. monocytogenes >122 34 Vacherin Mont d’Or cheese** France, 1995 L. monocytogenes 20 4 Brie de Meaux cheese** Canada, 1984 Salmonella Typhimurium 2700 1 Cheddar cheese** Switzerland, 1985 Salmonella Typhimurium >40 0 Vacherin Mont d’Or cheese** England, 1989 Salmonella Dublin 42 0 Irish soft cheese** USA, 1989 Salmonella Javiana and S. Oranienberg 164 0 Mozzarella cheese France, 1993 Salmonella Paratyphi B 273 1 goat’s milk cheese** Netherlands, Denmark, Sweden,USA, 1983 Enterotoxigenic Escherichia coli >3000 NR Brie cheese*** Scotland, 1994 Verotoxin-forming E.coli 0157 >20# 0 local, farm-produced cheese** Scotland, 1984–85 Staphyloccus aureus enterotoxin >13 0 sheep milk cheese** England, 1988–89 Suspected Staphylococcus aureus enterotoxin 155 0 Stilton cheese** Malta, 1995 Brucella melitensis 35 1 Soft cheese** * Pasteurised milk was used, but there was evidence that unpasteurised milk was also included. ** These products are known to have been produced using unpasteurised milk. *** Many Brie cheese are made from unpasteurised milk. NR: not reported, # one case of haemolytic uraemic syndrome. Data from Food Safety and Raw Milk Cheese. Professional Food Microbiologist Group of the IFST. Table 4.4 Helminths transmitted to humans in seafood Disease Causative organism(s) Seafood Small intestinal fluke infection Echinostomiosis Echinostoma spp Freshwater fishes Artyfechinostomum Freshwater fishes, prawns, malayanum crabs, freshwater snails

Heterophyiosis Heterophyes heterophyes Brackish water Heterophyes spp. Fishes, mullet Metagonimus yokogawaia Trout Liver fluke infection Clonorchiosis Clonorchis sinensis Freshwater fishes Opisthorchiosis Opisthorchis felineus Freshwater fishes Opisthorchis spp. Fishes Lung fluke infection Paragonimiosis Paragonimus westermani Fishes, crabs, crayfish, prawns, mammals Paragonimus spp. Crabs, crayfish, prawns Broad fish tapeworm infection Diphyllobothriosis Diphyllobothrium spp. Marine and freshwater fishes Larva migrans Gnathostomiosis Gnathostoma spinigerum Freshwater fishes, frogs, snakes, birds Gnathostoma spp. Freshwater fishes Eosinophilic meningoencephalitis Angiostrongyliosis Angiostrongylus cantonenesis Snails, fish, crabs, shrimp, frogs Visceral larval migrans Angiostrongyliosis Angiostrongylus costaricensis Mollucs Gastrointestinal invasion Anisakiasis Anisakis spp. Marine fishes, octopus, squid Pseudoterranova spp. Contracaecum spp. Phocascaris spp. Intestinal capillariosis Capillariosis Capillaria philippinensis Marine and freshwater fishes

a M. takahashii, H. nocens, H. dispar, Heterophyopsis continua. Pygidiopsis summa. Stellant chasmus falcatus. Centrocestus armatus and Stictodora fuscatum are known from Korea Source: Emerging problems in seafood borne parasitic zoonoses. Food Control, 1992, 3:2–7.

47 Hazards associated with different foods and their control

by fishborne parasites has been severely rounding water, at the same time accu- under-reported in the past and its extent mulating microorganisms from their en- as a food safety problem is only just vironment. Since they are mainly har- emerging. Travel and changing food hab- vested from shallow coastal waters where its mean that it is not a problem confined sewage contamination is likely to be to developing countries, the incidence of greatest, they are commonly contami- anisakiasis, for instance, is increasing in nated with pathogenic bacteria and vi- the United States. Although parasites will ruses of human (and animal) enteric ori- be readily killed by thorough cooking, in gin. Numbers of pathogenic bacteria in many countries raw, lightly cooked or their tissues can be reduced by transfer- marinaded fish can be common. These ring the shellfish to clean coastal waters preparation practices, which are being (relaying) or by holding them in tanks in used more widely, do not guarantee elimi- which the water is recirculated and dis- nation of parasites. infected with ultraviolet light (a process Fish from warmer coastal waters can of- known as depuration). While this is an ten be contaminated with the bacterium effective and well proven procedure for Vibrio parahaemolyticus and this can be bacteria, it is far less so for viruses which transferred to other fish both at the mar- seem to persist much longer in shellfish ket and in the home. V. parahaemolyticus tissues under these conditions. is readily killed by thorough cooking but Fish can also be the cause of a number can be spread to cooked fish by inad- of different intoxications where cooking equate separation of raw and cooked does not eliminate the problem. These products. Vibrio vulnificus is associated toxins are often the products of algae. with seafoods, particularly oysters, which When these algae are consumed by fil- are often eaten uncooked. It does not ter-feeding shellfish or small herbivorous cause diarrhoea but is responsible for very fish, the toxin accumulates in the flesh severe extra-intestinal infections such as which may then be consumed and accu- life-threatening septicaemia in patients mulated by larger carnivorous fish, which who normally have some other underly- in turn may be eaten by humans. ing disease. Ciguatera is an example of this where the toxin (ciguatoxin) is produced by the Vibrio cholerae is often transmitted by dinoflagellate alga Gambierdiscus toxicus water but foods that have been in con- and then amplified through the food tact with contaminated water or faeces chain. This particular condition occurs from infected persons frequently also only with fish from tropical and subtropi- serve as a vehicle of infection. These cal regions but other types of would naturally include fish from con- dinoflagellate intoxication occur in cooler taminated water or washed with it after climates. Usually this follows an algal being caught. The organism would be bloom where environmental conditions killed by cooking but recent cases of lead to a sudden proliferation of the cholera in South America have been as- toxin-producing algae. A number of dif- sociated with the uncooked fish marinade ferent illnesses have been identified: para- ceviche. lytic shellfish poisoning caused by toxins Water polluted with sewage is a particular produced by the Alexandrium (Gonyaulax) problem with filter-feeding molluscan species and others; neurotoxic shellfish shellfish such as oysters and mussels poisoning, which follows so-called red which are often eaten raw or after only tides, caused by Ptychodiscus brevis; and light cooking. These feed by filtering nu- diarrhoeic shellfish poisoning caused by trients from large volumes of their sur- toxins produced by Dinophysis fortii (see

48 Basic Food Safety for Health Workers

Table 2.3). These types of foodborne ill- Problems with Clostridium botulinum have ness are controlled by monitoring for in- been encountered with some traditional cidents of algal blooms and banning the fermented fish products. These rely on a harvesting and sale of shellfish from the combination of salt and reduced pH for areas where they occur. their safety. If the product has insufficient salt, or fails to achieve a rapid pH drop Scombrotoxic fish poisoning is an intoxi- to below 4.5, C. botulinum can grow. cation that exhibits the symptoms of histamine toxicity. Scombroid fish such as tuna, bonito and mackerel have mainly been implicated although non-scombroid Fruits and fish such as sardines, pilchards and her- rings have also caused cases. It is thought vegetables that bacterial decomposition of the fish As described in Chapter 2, some fruits flesh leads to toxin production as freshly and vegetables can be hazardous as a re- caught fish have not been implicated. sult of their intrinsic toxicity. This prob- The toxin is heat stable since outbreaks lem is best avoided by using only those have been caused by canned fish. The plant products with a record of safe use potential toxicity of fish is assessed by and by employing well established meth- measuring the level of histamine present, ods for safe preparation (e.g. in cassava although this does not appear to be the processing). toxic agent since it has not proved possible to reproduce the symptoms in volun- Contamination from pesticide residues or teers fed histamine and some cases have other environmental chemicals may also been reported where the fish implicated pose problems. Such hazards are best contained low levels of histamine. controlled by using proper agricultural practices and protecting growing crops Fish products can pose a number of food from sources of environmental contami- safety hazards when critical steps in nation. processing are not adequately controlled. During cultivation, harvest and storage, For example, cooked products must al- fruits and vegetables may become ways be protected against contamination contaminated with pathogens from after cooking. In commercial fish prod- sources such as water, soil and animal or ucts, one example where this has been a bird excreta. The risk of such particular problem is frozen, peeled, contamination can be greatly increased cooked prawns, where pathogens can be as a result of practices such as using introduced during the extensive handling manure or human sewage as a fertilizer of the product after cooking. or irrigating with sewage-polluted water. In many fish products, salt is an impor- The problem is likely to be worse in those tant factor in limiting the growth of products that grow in or very near the pathogens. For example, pre-salting is a ground. The liver fluke Fasciola hepatica common practice in fish drying where it has been transmitted via watercress as a helps accelerate drying while limiting the result of contamination of the growing growth of bacteria during the process. In beds with cattle or sheep manure. smoked fish, a minimum salt content of Species of Bacillus, Clostridium and Listeria 3% in the water phase and an internal monocytogenes can all be introduced from temperature of at least 63oC during the soil, while the full range of enteric smoking have been recommended in or- pathogens spread by the faecal-oral route der to control Clostridium botulinum. (parasites such as Entamoeba histolytica and

49 Hazards associated with different foods and their control

Giardia, viruses such as rotavirus, illness. This is a food safety problem Norwalk-type agents, hepatitis A virus, mainly in the case of vegetables because and bacteria such as Shigella, Salmonella, their tissues are less acidic than those of E. coli and Vibrio cholerae) can all be in- fruits. It is a particular concern in the troduced as a result of contamination by commercial production of pre-prepared sewage. salad vegetables which are more exten- Once again, cooking will eliminate all but sively handled and processed than most the sporeforming bacteria and these may other products. This means that great grow if the cooked product is stored care has to be taken in the sourcing and unrefrigerated for extended periods. For hygienic processing of ingredients. In example, wrapping pre-cooked potatoes acidic products like citrus fruits, the pH or other root crops in aluminium foil is generally too low to support the growth creates anaerobic conditions and could of pathogens and damage simply results lead to the growth of Clostridium in spoilage by more acid-tolerant botulinum. organisms such as yeasts and moulds. Pathogens can, however, survive on the Contamination on fruits and vegetables outer surfaces of these products. that are eaten without cooking can be Mouldy products will already have had reduced by washing them thoroughly with their antimicrobial barriers breached. This clean water. Inclusion of a disinfecting can lead to bacterial growth but can also agent such as hypochlorite in the water result in contamination with mycotoxins can improve the elimination of produced by moulds. Mycotoxins are microorganisms associated with the mainly associated with products such as product but this does not guarantee cereals and oilseeds but contamination safety. The surface of many fruits and of fruit and vegetables is also known. The vegetables is not smooth and has many mycotoxin patulin produced by several small indentations where microorganisms species of Penicillium is most often may “hide”, remaining on the product associated with moulded apples. It can even after quite extensive washing. If the also contaminate juices made from water used to wash fruit or vegetables is moulded fruit. Toxigenic strains of the contaminated, this can, of course, have species Fusarium have been isolated from precisely the opposite effect and bananas and the mycotoxins introduce dangerous contamination. diacetoxyscirpenol and zearalenone have Microbial growth on intact fruits or sometimes been detected at very high vegetables will be limited because the levels. Aflatoxin contamination has also plant possesses natural antimicrobial been found on occasion in dried fruits barriers in the form of the skin, shell or such as raisins and figs. rind which protect it from infection during life. The plant surface is a relatively Mould infestation does not always inhospitable environment for most indicate contamination with mycotoxins, pathogens and they will not be able to and conversely mycotoxins can grow, though they may survive. Any sometimes be present in a product in the damage that breaches these antimicrobial absence of any obvious moulding. As a layers will lead to microbial invasion and general precautionary measure, obviously growth in the underlying tissues, so any mouldy foods should be avoided. form of processing such as chopping, slic- Traditional forms of processing such as ing or peeling will increase potential for pickling and fermentation rely on acidic the growth or survival of contaminants conditions to ensure the safety and keep- and the risk of transmission of foodborne ing quality of a food product. At low pH,

50 Basic Food Safety for Health Workers pathogens will not grow and will die dur- caused by Staphylococcus aureus in pasta ing storage. Procedures such as drying will occurred when the starchy dough was not remove pathogens though they will contaminated with the organism and left not grow on the dried product. Sun-dry- too long, allowing growth and toxin pro- ing could, however, result in the introduction before drying. In many African duction of pathogens through contami- countries, a cereal porridge is a staple nation from birds, flies or rodents. food and post-cooking contamination of this has been implicated as a vehicle in the transmission of weanling diarrhoea Cereals and cereal by a number of different pathogens. In some areas these porridges traditionally products undergo a lactic fermentation and there is evidence that this is a useful way of Mycotoxins are the main food safety improving the safety of these products. hazard associated with cereals and their The lactic acid and low pH in these products. Cereals can be infected with porridges has been shown to inhibit a mycotoxigenic moulds, sometimes in the wide range of bacterial pathogens and one field, but more commonly during study has suggested a lower incidence of improper storage. These toxins can persist diarrhoea in children where fermented through processing into the final food porridges are consumed (17). product. Bacteria are less of a direct threat since the low moisture content of cereals during storage prevents their growth. Bottled waters Organisms such as Salmonella may The importance of polluted water as a occasionally be present as a result of source of pathogenic organisms has been faecal contamination but the bacteria discussed briefly in Chapter 3 and the most commonly found surviving on beneficial impact of supplies of clean cereals and their flours are species of the safe water on public health is difficult to sporeformer Bacillus. overstate. Bottled waters are produced Cereal products are nearly always cooked throughout the world and are increasingly before consumption to gelatinize the popular in many countries. These are starch and make them more palatable and generally produced from water that is digestible. This will also eliminate the completely free of pathogenic organisms. non-sporeformers from the product. If For example, natural mineral waters the cooked product has a sufficiently high within the European Union must come water activity and is stored at an from a specified underground source that appropriate temperature, the spores of is protected from any kind of pollution. Bacillus cereus and other toxigenic Bacillus Other types of bottled water can be species can germinate and grow to cause produced from alternative sources, illness. There is a common association of including the public water supply. The foodborne illness from Bacillus species sources used naturally tend to be those with starchy products such as rice and that are unpolluted and this should be pasta dishes, sauces thickened with confirmed by microbiological analysis. cornflour and various breads. After abstraction such waters can also be Starchy suspensions in water make an subjected to disinfection treatments, usu- excellent growth medium for almost any ally involving a combination of filtration, bacterial pathogen if it is introduced. A ozonization and irradiation with ultravio- large international outbreak of illness let light. Where bottled waters are car-

51 Hazards associated with different foods and their control

bonated this too has a strong antimicro- isms in the bottles can produce visible bial effect. As a result bottled waters growth during prolonged storage of the have a very good health record. One no- product, though this is generally more of table exception to this was when bottled an acceptability problem than a health water was implicated as a vehicle of in- hazard. One Japanese survey of im- fection in a cholera outbreak in Portugal ported and home-produced bottled wa- in 1974 (18). ters found visible microbial growth, prin- Though the water used may be very pure cipally mould growth, in 20% of the sam- microbiologically, this may not always be ples examined (19). true of the bottles that are used. Organ-

KEY POINTS

l Raw foods can contain pathogens from a variety of sources.

l Animal products are the most likely foods to contain pathogens.

l Plant products may also be contaminated with pathogens, particularly if they have been exposed to sewage or sewage-contaminated water.

l Correct processing can help control the growth/survival of pathogens.

l Cooking/heating is the most effective and reliable way of improving food safety.

l Commercially canned foods are generally safe.

l Good hygiene rules must be followed regardless of the food being processed.

52 Basic Food Safety for Health Workers

Chapter 5 Technologies for the control of hazards

Some of the safety implications of food processing were introduced in Chapter 4 Technologies when discussing individual food types. However, since many food processing that prevent technologies are applied to various kinds of food, some general principles are best contamination illustrated by considering the technologies themselves. Packaging Food preservation technologies are intended to improve the keeping quality The living animal or plant which is used and safety of food commodities. In most to make a food product has physical an- cases this is done by influencing in some timicrobial barriers such as the skin, shell, way the microorganisms that cause husk or rind to protect it from infection. spoilage and foodborne illness. The These are often removed or damaged technologies can be classified according during processing to expose the underly- to how they affect the microorganisms, ing nutrient-rich material that can serve namely: as an excellent medium for microbial growth. Packaging to some extent re- places these natural barriers. Traditional n technologies that prevent contamina- approaches are still common, such as the tion; widespread use of banana leaves for packaging foods in tropical countries, the n technologies that control microbial covering of cheeses in wax or immersing growth; them in oil, and the wrapping of comminuted meat products in animal intestines. n technologies that remove or kill Modern technology has added numerous microorganisms in food. types of metal, glass, plastic and paper packaging to supplement these. These are useful distinctions but there are Generally the effect of packaging has often areas of overlap. been to improve food safety by protect-

53 Technologies for the control of hazards

ing the food from contamination. Con- Cleaning and disinfection of cern has been expressed about the migration of compounds present in pack- equipment and utensils aging into some foods but, provided food-grade packaging materials are used, the levels of the compounds detected are The equipment used in food processing minute and probably toxicologically can act as a source of contamination if it insignificant. Lead soldered cans were is not thoroughly cleaned and disinfected. once an important source of dietary lead Cleaning has two objectives — removal but this has been controlled by the of food residues adhering to the equip- replacement of lead solder with ment which can support the growth of electrically welded or two-piece cans. microorganisms, and removal of viable microorganisms. Both objectives can nor- Packaging sometimes also plays an im- mally be achieved by washing in very hot portant role in controlling the growth of water (around 80oC) or thorough wash- microorganisms already present in the ing with water and detergent followed by food when it is packed. In vacuum or a sanitiser such as hypochlorite, iodophors modified atmosphere packaging, the or quaternary ammonium compounds to packaging film is chosen for its gas per- eliminate microorganisms that may still meability properties which determine be adhering (Figure 5.1). whether it can retain an atmosphere inside the pack that is inhibitory to the growth of spoilage organisms. This can sometimes have safety implications since pathogens in general are little affected by this type of storage. Recog- nition of spoilage can be a warning of a potential safety risk since it signals that storage conditions have allowed extensive microbial growth to occur. If pathogens are unaffected by a packaging technology but spoilage is less obvious or de- layed, there is an increased risk that unsafe foods will be consumed. This has led to outbreaks of botulism caused by vacuum- packed smoked fish in the past. Figure 5.1 Cleaning and disinfection

54 Basic Food Safety for Health Workers

Hygienic design of equipment the water will be ice). When foods are frozen some of the bacteria are killed or To ensure that equipment can be easily injured but many will survive and can disinfected it must be designed and built resume growth if the food is defrosted with hygiene in mind. This will mean that and stored at a temperature within the it is free from pockets or crevices where danger zone. Helminths such as Anisakis food can accumulate and serve as a fo- and Clonorchis in fish and Trichinella and cus of infection, that it is easy to clean Taenia in meat are much more sensitive and disinfect, and that it is made from and can be killed by frozen storage at materials that will not contaminate the -20oC for seven days. In this context, food and are unaffected by the cleaning freezing can be considered as a technol- and sanitizing agents used. ogy that eliminates a hazard. It is therefore of great potential importance in controlling foodborne helminth infections in Technologies that countries where raw or lightly cooked fish and meats are eaten. control microbial Many traditional food products rely on acidity to reduce the pH and inhibit the growth growth of pathogens and spoilage Chapter 3 described the factors that organisms. This acidity can be added in influence microbial growth. Many food the form of vinegar (acetic acid) as in preservation technologies, both many traditional pickled products; lime traditional and modern, are based on the or lemon juice (citric acid) as in some manipulation of one or several of these marinades and dressings; or it may be factors to inhibit microbial growth in generated by lactic acid bacteria growing food. in the product to produce lactic acid as occurs in cheese, sauerkraut, yoghurt and Decreasing the temperature can prevent salami production. At pH values where or slow the growth of microorganisms growth is prevented, microorganisms will depending on the temperature and the eventually die though this can be quite a microorganisms concerned. Chill tem- slow process, particularly at chill temperatures (< 8o) will prevent the growth peratures. It is therefore safest to regard of mesophilic bacterial pathogens such acidification as a process which reduces as Salmonella, Shigella, E. coli and Clostrid- risk rather than eliminates it. ium perfringens and psychrotrophs such as Reducing the water availability/activity Listeria monocytogenes will grow only rela- in a food by drying, salt-curing or tively slowly. Chilling does not necessar- conserving in sugar will also inhibit ily eliminate a hazard though it can help microbial growth. This is a widespread control it. If the pathogen is present in traditional food preservation technique. high numbers before chilling, or if chill Microorganisms will generally survive temperatures are not maintained through- this process even if they cannot grow in out the storage period, a chilled food may the final product. They could therefore still cause illness. resume growth if the product is Microorganisms will not grow at tempera- rehydrated or stored in a moist tures below about -10oC. Frozen storage environment where water will condense on the product increasing its a . prevents their growth by the combined w effect of the low temperature and the low Modified atmosphere packaging and water availability/activity (since much of vacuum packaging of foods inhibit the

55 Technologies for the control of hazards

growth of some microorganisms, principally those associated with spoilage, by Technologies that increasing the level of carbon dioxide in the pack. Since maintenance of the ap- remove or kill propriate gas atmosphere around the food depends on the packaging material, microorganisms in some of the safety implications of modified atmosphere packaging and food vacuum packaging have already been discussed above. Other antimicrobial agents such as nitrite, Heat treatment the bacteriocin nisin and benzoic acid are Various forms of cooking such as boiling, used in foods where their contribution is frying, roasting and baking have been usually the inhibition of specific groups used since earliest times to improve the of organisms. Their effect is also often palatability, digestibility and safety of dependent on other environmental foods. Even today, heat treatment remains factors such as temperature and pH and the most accessible and effective method illustrates an important concept in food of ensuring that food is free from preservation — the multiple barrier or pathogenic organisms. Failure to deliver hurdle concept. Changing a single factor a sufficient heat process is often that affects microbial growth in order to identified as a causative factor in preserve a food often causes major outbreaks of foodborne illness. changes in the food’s characteristics and these are not always acceptable to the The way in which we describe and meas- consumer. Acceptable shelf life and ure how effectively a heat process kills safety can often be achieved by adjust- microorganisms is described in Chapter ing a number of factors simultaneously. 3. Heat treatments that kill only the veg- Each on its own is not sufficient to pro- etative forms of pathogens are called duce a useful inhibition of spoilage and/ pasteurization. These can be applied to or pathogenic organisms but their cumu- ensure the safety of liquid food products lative effect is. Many traditional products such as milk, liquid egg and ice cream are examples of the practical application mix, and the precise combination of time of the hurdle concept. For example, the and temperature required to do this is shelf life and safety of fermented meats normally prescribed in a regulation (see such as salami depends on reductions in Table 4.2). Pasteurization is also used to pH and water activity through drying and extend the shelf life of products such as salting, the antimicrobial effect of nitrite fruit juices, alcoholic and non-alcoholic and, in some cases, the preservative drinks, pickles and sauces. The food value of the chemicals deposited on the safety risk from these products is usually product as a result of smoking. Depend- very small due to other antimicrobial fac- ing on the precise formulation, each of tors, particularly pH, though occasional these can make a different contribution. outbreaks have been reported, such as an Where the aggregate effect is insufficient, outbreak of E. coli O157 infection in the additional hurdles such as low tempera- USA from contaminated apple juice. ture storage can also be employed. Simi- lar multiple hurdles can be identified in Wherever it is applied, therefore, pasteuri- cured meats, smoked fish, conserves and zation provides an additional guarantee many other products. of safety.

56 Basic Food Safety for Health Workers

Outbreaks of foodborne illness caused trolled to ensure that it achieves the de- by pasteurized foods such as milk are sired reduction of bacterial spores. The generally the result of one of two possible principal food safety concern is that in failings: low-acid foods (pH >4.5) the heat process must eliminate spores of Clostridium n failure to apply a heat process sufficient to kill all vegetative pathogens botulinum. A minimum heat process, present; known as a botulinum or 12D cook, is prescribed which reduces the number of n contamination of the product after C. botulinum spores by a factor of 1012 pasteurization from an unpasteurized (1000 billion). In fact, to reduce the product or from some other number of spores of spoilage organisms environmental source of pathogens. present to acceptably low levels, the heat Heat treatments more severe than pas- process applied in practice is often far in teurization are also applied to foods. excess of this safety minimum. Where the These kill all microorganisms capable of pH of the food is less than 4.5, Clostrid- growth in the food under normal ium botulinum will not grow even if the conditions of storage, including the more spores survive and so a milder heat proc- heat-resistant bacterial spores, resulting ess can be used. Safety problems can arise in shelf-stable products. These foods are when low acid (pH >4.5) foods are described as being “commercially sterile” canned or bottled at home where the or appertized. Two techniques are used potential safety problems are less well to produce appertized foods: canning and understood and control is less stringent. UHT processing coupled with aseptic A number of outbreaks of botulism have packing. been associated with home-bottled vegetables in the past. Canned foods When the hot cans are cooled after processing, a vacuum is created inside the All the food groups described in Chapter can which could result in contamination 4 can be processed into canned foods. being sucked in from outside. An These have an extremely good safety outbreak of typhoid fever was caused in record and can normally be consumed, just this way when cans of corned beef with or without reheating, with little fear were cooled in contaminated river water. of their causing illness. The product is To prevent this from happening, clean packed into a container, normally a tin- chlorinated water should always be used plated can, sealed and then given a heat for cooling. process far in excess of normal cooking which eliminates both the spores and the vegetative bacteria capable of causing spoilage or illness. This requires heating the product in the can to temperatures in excess of 100oC (normally around 121oC) for several minutes. It means that the product is stable for long periods without refrigeration. Problems could arise if the product is insufficiently heated or if it is contaminated after heat processing. Commercially, the heat process is carefully designed, monitored and con-

57 Technologies for the control of hazards

Cans are protected from recontamination Physical damage or deterioration of the by the strength and integrity of the can could also lead to contamination of container. A key part of this is the its contents. Often microbial growth in a complex double seam which joins the can can will become apparent when gas is lid to its base (Figure 5.2). Checking the produced and the end of the can swells. Food from cans which have deformed in this way should not be eaten. However, this may not always happen so food must also be discarded when it comes from cans that are dented or rusty or where the food appears “off” once the can is opened. If they are not used immediately on opening, the contents of a can should be transferred to a clean dry container for storage. Food should never be left in an open can as this can lead to increased uptake of tin from the container. UHT processing/aseptic packaging In these processes the food is heat-treated before being packaged in a previously Figure 5.2 The double seam can sterilized container in a sterile environment. By heating the product separately its temperature can be increased much seam to ensure that it is correctly formed more quickly, often to temperatures is an important safety control measure. higher than those used in canning, and To do this thoroughly requires some this reduces quality losses in the product expertise but gross failures are more while retaining the same antimicrobial readily detected (Figure 5.3). effect. The packaging material is usually a plastic or laminate film that is formed into containers in the packaging machine, though sometimes preformed containers are also used. In most commercial equipment the packaging is sterilized by hot hydrogen peroxide. UHT processing is applied mainly to liquid foods such as milk, soups and fruit juices because they heat up very quickly as a result of convection. If a food contains particles that heat up by conduction, the process is slower and some of the advantages of UHT processing are lost. New techniques such as ohmic heating which will heat particulates rapidly promise an extension Figure 5.3 Defects in can seams of UHT processing to other foods.

58 Basic Food Safety for Health Workers

Ionizing irradiation Ultraviolet irradiation Specific applications of radiation treat- Ultraviolet light can kill microorganisms ments are now permitted in more than but, unlike ionizing radiation, its penetrat- 35 countries. These include the treatment ing power is very limited. Its use is re- of meat, poultry, eggs and shrimps to stricted to disinfecting surfaces and also remove parasites and Salmonella and the reducing the population of airborne fun- decontamination of food ingredients such gal spores in areas where they would pose as spices and herbs. Parasites are more a threat to a product’s shelf life (e.g. in sensitive to irradiation than bacteria and bakeries). doses as low as 0.3 kGy can render them non-infective. Bacterial spores are Washing and disinfection relatively resistant (Table 5.1). Washing with clean water will remove At the low doses allowed to remove veg- some of the microorganisms adhering to etative forms of bacteria (<10 kGy), no the surface of a food product. The num- perceptible changes are produced in the bers of microorganisms on the food can food so it retains the characteristics of be reduced still further if the water used the raw product. contains an antimicrobial compound such as chlorine which will kill some of those Concerns over the potential safety of that remain attached to the surface. food irradiation have been extensively Washing fruits and vegetables is an ob- investigated and found to be without vious example of this. While it is a use- foundation. Despite its undoubted poten- ful and effective safety measure for re- tial to contribute to food safety, commer- ducing gross contamination, microorgan- cial uptake of irradiation has been lim- isms in surface pockets inaccessible to ited because of consumer resistance to the water and antimicrobial will be unaf- the concept of irradiated foods. fected.

Table 5.1 Dose requirement in various applications of food irradiation Purpose Dose (kGy) Products Low dose (up to 1 kGy) Inhibition of sprouting 0.05-0.15 Potatoes, onions, garlic, gingerroot, etc. Insect disinfestation and parasite 0.15-0.50 Cereals and pulses, fresh and dried fruits, disinfection dried fish and meat, fresh pork, etc Delay of physiological process 0.5-1.0 Fresh fruits and vegetables (e.g. ripening) Medium dose (1-10 kGy) Extension of shelf-life 1.0-3.0 Fresh fish, strawberries, etc. Elimination of spoilage and pathogenic 1.0-7.0 Fresh and frozen seafood, raw or frozen microorganisms poultry and meat, etc. Improving technological properties of food 2.0-7.0 Grapes (increasing juice yield), dehydrated vegetables /reduced cooking time), etc. High dose (10-50 kGy) Industrial sterilization (in combination with 30-50 Meat, poultry, seafood, prepared foods, mild heat) sterilized hospital diets Decontamination of certain additives and 10-50 Spices, enzyme preparations, natural ingredients gums, etc.

59 Technologies for the control of hazards

Washing meat carcasses with solutions chlorine-based sanitizer to a point where of organic acids such as lactic acid has there is residual free chlorine detectable been used in some countries as a means in the water. Some pathogenic protozoa of reducing surface contamination. such as Cryptosporidium show a marked Leaving foods wet after washing can ac- resistance to chlorine and can be effec- tually encourage microbial growth as the tively removed from water only by filtra- availability of water will be increased for tion. Therefore to produce a safe water those microorganisms that have survived combination of filtration and disinfection the treatment. is recommended. Water itself can be disinfected by boiling or by the addition of chlorine or a

KEY POINTS

l Food preservation technologies can be classified according to their effect on microorganisms.

l Some technologies prevent contamination.

l Some technologies control microbial growth and production of toxin.

l Some technologies remove or kill microorganisms in food.

l If correctly applied, these technologies improve the keeping quality and safety of food.

l Processes that kill microorganisms give the greatest certainty of food safety.

l Heat treatment is the most effective and accessible method of killing microorganisms in foods.

60 Hygiene in food preparation

68 Basic Food Safety for Health Workers

KEY POINTS l Application of general rules governing food hygiene can improve food safety. l WHO’s Ten Golden Rules for Safe Food Preparation summarize the most important aspects of food hygiene. l More detailed rules are required for mass catering than for domestic food preparation. l Hygiene rules govern physical, operational and personal factors. l Health workers can play an important role in educating food handlers in food hygiene. l General rules suffer from a lack of specificity. l Microbiological testing of food, while specific, is ineffective as a routine tool for assuring food safety. l Application of procedures that are both preventive and specific such as HACCP are the most effective way of protecting food safety.

67 Hygiene in food preparation

other organisms that might indicate the oped. The most commonly implemented presence of pathogens. This is a totally of these is known as the system of unrealistic option for domestic and small- Hazard Analysis and Critical Control scale food preparation and, while at first Point (HACCP). sight appealing, it has been discredited HACCP involves the systematic evalua- even for large-scale food production. It tion of a specific food processing or is now almost universally recognized that preparation procedure to identify hazards microbiological testing of food products associated with ingredients or the on its own is an ineffective and expen- processing procedure itself and to find sive way of trying to achieve an accept- out how those hazards can be control- able level of food safety assurance. led. It then decides which steps in the Microbiological testing can be very costly process are essential to controlling haz- and only gives information after the ards so that attention can be focused on event, when the problem has already them. arisen. It may also give a false sense of While this system was first applied to security since microorganisms will not be commercial food processing, it can also spread uniformly throughout a food and be applied to any operation where food samples taken may not show the pres- is handled or processed for consumption. ence of pathogens even though the food It is also replacing traditional regulatory is contaminated. Even when pathogens approaches. Many countries now recog- are detected, this will not necessarily in- nize HACCP in their food safety regula- dicate where the problem arose and how tions and their enforcement procedures it can be solved. Without this informa- are being adapted to ensure that food in- tion, the same problem is likely to recur dustries apply HACCP in a systematic again and again. way. A far better approach is to control micro- The full rigours of a HACCP system, as biological quality at source, during pro- outlined in Appendix 3, are probably not duction or preparation, so that safety is feasible or even necessary in households, built into the product. Put simply, it is but the essence of the approach — much better to prevent a problem from identifying hazards and the key steps that arising than try to remedy the situation will ensure their control is useful both at after it has. Food hygiene rules attempt the level of the household and more to do this but lack the specificity required. generally in health education campaigns To overcome this problem, new preventa- and courses. tive approaches have had to be devel-

66 Basic Food Safety for Health Workers leave the worker financially worse off as it would then be a disincentive to the The Hazard honest disclosure of any symptoms. A person suffering from diarrhoea should Analysis and not be allowed to handle open food. If food is to be handled by a person with Critical Control spots or infected cuts or skin lesions, these should be covered with a water- Point (HACCP) proof dressing. system It is not necessary for a food handler to have an overt infection in order to pose a threat to food safety. The asymptomatic Where general rules of good food carriage of Staphylococcus aureus on the hygiene are followed, they establish a skin, in the nasopharynx and hair folli- baseline of good practice in food cles has already been described. Activi- preparation that can play an important ties that encourage hand/mouth contact role in ensuring food safety. The strength such as smoking or the chewing of gum, of such rules lies in their general tobacco, betel nut or finger nails can also applicability, but this can also be a source therefore lead to food contamination and of weakness. In attempting to cover all must be avoided. The same also applies circumstances, some rules may seem to the tasting of food during preparation. vague, or even irrelevant or unrealistic Similarly, food handlers should not spit, in certain situations, and to some this can sneeze or cough over food, or pick their appear to devalue the whole approach. nose, ears or any other parts of their body. Individual food preparation activities, both domestic and on a larger scale, have Many of the basic rules of food hygiene their own characteristics: they do not all are already observed as part of traditional produce the same products, and they use religious or cultural habits that go back different raw materials, different thousands of years, but the reasons for processes and different equipment. What their importance in terms of food safety food handlers really want is guidance on are often not clearly understood. It is easy food safety related to their own specific for lapses to occur resulting in a threat to operations. Precisely how should they food safety. Education of food handlers store their raw materials? What are the in basic food hygiene is important so that most important areas to clean and when rules are not seen as pointless irritants (sweeping a dusty floor, for instance, is dreamed up by bureaucrats. If food cleaning but it can actually increase handlers understand the reasons for the contamination of exposed food)? How rules, this will encourage them to apply long should the food be cooked? In what the rules rigorously and consistently. For order should ingredients be added? These the general population, basic food hygiene and many other questions are often of education can focus on WHO’s Ten golden great relevance to food safety and require rules but more detailed training is required specific answers. for food handlers in mass catering. In this educational process, the health worker One approach to checking the safety of can play a significant role. This is one of particular foods would be to test them to the issues addressed in Chapter 7. see if they contain specific pathogens or

65 Hygiene in food preparation

to ensure that all parts reach a tempera- in food is not just aesthetically objection- ture of at least 70oC. Precooked foods able but may also be a source of patho- should be stored outside the temperature gens. danger zone of 10–60oC and those served hot should be reheated to 70oC before Personal factors: consumption. If frozen meat and poultry are not com- personal pletely defrosted before cooking, some parts may not get hot enough to kill the hygiene and training pathogens present. As indicated in Chapter 3, the food When dishes containing a mixture of handler can often be a major source of cooked and raw ingredients are being contamination. There are several good prepared, it is important to cool the hygienic practices that he or she should cooked component before mixing with observe. the other ingredients. Failure to do this could lead to a temporary rise in tempera- Hands should be washed regularly with ture during which microbial growth can soap in clean water, but especially before occur. starting to handle food, after going to the toilet or changing a baby, and after The other major objective of hygienic handling raw food, food waste or food handling is to avoid contamination, chemicals. In all these activities the hands particularly of cooked or ready-to-eat may become contaminated with foods. Physical measures such as the pathogens or toxic chemical residues that exclusion of vermin from the premises can then be transferred to the food. It is contribute to this, as do a number of easier to keep hands clean if finger nails operational procedures such as keeping are kept short and jewellery such as rings food covered as much as possible. are removed as dirt can become lodged The liquid that accumulates during the under these and may be difficult to defrosting of frozen meat is likely to remove. contain pathogenic microorganisms. It Food handlers should avoid coughing into must not be allowed to drip on other their hands or touching their hair, nose foods stored below it and great care must or mouth while handling food without be taken in disposing of it. Any washing their hands afterwards. equipment or surfaces contaminated during defrosting must be thoroughly Routine medical and microbiological ex- cleaned and disinfected. amination of food handlers is not generally recommended but if food handlers Cooked food should be kept well are suffering from an illness that includes separated from raw food to reduce the symptoms such as jaundice, diarrhoea, risk of cross-contamination. vomiting, fever, sore throat, skin rash or Touching cooked foods with bare hands skin lesions such as boils or cuts, they should be avoided wherever possible as should report this to their supervisor be- even clean hands can carry pathogenic fore starting work. It may then be neces- microorganisms. Ideally, hair should be sary for them to be assigned temporarily covered or at the very least tied back to some other task which does not in- when one is working in a kitchen. Hair volve handling food. This should not

64 Basic Food Safety for Health Workers clean. In commercial food processing this confusion between poisonous substances is overcome by using an antimicrobial and food materials. Rubbish and waste agent (a disinfectant or sanitizer) as well should also be stored away from the food as a detergent to clean food contact sur- preparation area. faces. This can be expensive and unnec- The importance of not leaving food for essary at the household level. Heat is the extended periods at temperatures in the most effective antimicrobial agent and danger zone at which microbial growth thorough washing with hot water (more o can occur has been referred to earlier. The than 80 C), perhaps with a small amount equipment used to cool food is of of detergent, will clean a surface and kill obvious importance here. For example, those microorganisms that are not easily shallow trays allow faster cooling of removed (Figure 5.1). Frequent cleaning foods and are preferable to deeper is also important since dried and en- containers. Cold storage equipment crusted residues are much harder to re- should be well maintained and checked move. regularly to ensure it operates at the Cloths used for cleaning can rapidly ac- correct temperature. If cold storage cumulate a large population of microor- equipment is overloaded this will slow ganisms, particularly when left moist, and down the cooling process and the food their use can actually increase contami- will spend longer in the temperature nation rather than reduce it. They should danger zone. therefore be changed every day and Similarly, cooking equipment should be boiled before re-use. adequate for its intended use, well We have already seen how raw foods can maintained and checked regularly to act as a source of pathogens. It is confirm that it is functioning correctly. important, therefore, that the layout of To allow good personal hygiene, the the premises and equipment should allow premises must have adequate and foods to be stored and handled without hygienic toilet facilities separated from contact between raw and cooked prod- the food production area, as well as ucts, either directly or via equipment. adequate hand-washing facilities. The food should also be protected from other sources of contamination such as soil, insects, rodents and other animals Operational factors: (wild or domesticated). For this reason, food should not be placed on or near the hygienic handling ground in open containers. As far as possible, the premises should be of food protected to prevent pests entering. This is sometimes very difficult in the A large part of the hygienic handling of household so storing foods in tightly foods relates to the correct use of sealed containers is an effective second temperature in the control of line of defence. microorganisms — avoiding temperatures where microbial growth is Facilities should also be available for possible and, where appropriate, ensuring storing dangerous or toxic substances that temperatures are sufficiently high to such as disinfectants and insecticides kill microorganisms. For example, outside the kitchen area in a clearly perishable foods should normally be marked location. This will minimize the stored refrigerated at <10oC. Food that risk of accidents occurring as a result of are cooked should be cooked thoroughly

63 Hygiene in food preparation

Figure 6.1 Principle components of food hygiene

Physical factors: A first requirement is that the working environment should be well lit, well ven- premises and tilated and tidy as this will encourage good working practices and promote food safety. The working environment should equipment also be clean and easy to clean. Microor- Ideally, food preparation premises should ganisms can grow on any scrap or parti- be purpose built and sited in an area that cle of food remaining on food contact is free from objectionable odours, smoke surfaces or lodged in some crack or crev- and dust, is located away from rubbish ice and this can act as a source of con- tips, and is not prone to events such as tamination. While most microorganisms flooding. In practice one usually has a will be associated with food particles that more limited choice about the building can be removed by thorough physical to be used and its location, but it should cleaning, it should be remembered that a be of sound construction and well surface may appear physically clean al- maintained. though it may not be microbiologically

62 Basic Food Safety for Health Workers

Chapter 6 Hygiene in food preparation

Chapter 3 describes the principal sources work, in hospitals and educational of food contamination and these are establishments, at social gatherings and so mentioned again in the discussion of the on. The scale of mass catering means that safety of particular food commodities in breakdowns in good hygienic practices can Chapter 4. Clearly it is important to be have far more serious consequences in aware of specific problems associated terms of the number of people affected with certain foods. However, in many and, sadly, events involving mass catering cases, food safety can be enhanced by a often feature prominently in many national number of general measures, regardless statistics on outbreaks of foodborne of the food materials being handled. The illness. For these reasons a more extended most important of these have been for- list of food hygiene requirements directed mulated by WHO as a set of Ten golden at mass catering is given here. The reader rules for safe food preparation. These are pre- is also referred to other WHO publications sented in Appendix 2. These give guid- dealing specifically with this topic. (See ance to the general population on the bibliography) Many of the rules apply to essential principles of safe food prepara- food preparation at all levels, though some tion. are excessive and inappropriate to food preparation in the home. Some instances Though the Ten golden rules apply equally of this are highlighted. to all food preparation activities, catering on a larger scale is a more complex operation than preparing food for the Rules of good hygienic practices in food immediate family and requires more preparation deal broadly with three dif- detailed rules. It involves preparing larger ferent areas: physical factors relating to quantities of food for more people mainly the premises and equipment used, opera- using paid employees, special premises and tional factors relating to the hygienic han- equipment. It is also becoming increasingly dling of food, and personal factors relat- important as more people eat food that ing to questions of personal hygiene and has been prepared outside the home, at training (Figure 6.1).

61 The role of health workers in food safety

specific infections such as test for a range of pathogens. campylobacteriosis, salmonellosis, or E. Outbreak detection takes several forms. coli O157:H7 infection. Laboratory Health workers should keep alert to the surveillance involves the recording of possibility of a shared exposure among results of laboratory investigation of patients with the same condition, or they specimens (usually faecal samples) ob- may routinely report selected conditions tained from patients. The laboratory can either voluntarily or as required by law.

KEY POINTS

l Prevention is better than cure.

l Education in food safety is an important preventive measure.

l Educational programmes must be focused and relevant to the target audience.

l Specific target groups for food safety education should be identified and educational interventions aimed at them.

l Mothers and pregnant women are important target groups for prevention of infant diarrhoea.

l In addition to education of food handlers in basic principles of food hygiene, an HACCP-based approach can be applied to the preparation of food in homes, in food service establishments or for street food vending operations in order to select behaviours which are of particular importance to food safety.

l Surveillance of foodborne diseases is an important tool for assessing the food safety situation and identifying factors leading to foodborne diseases.

74 Basic Food Safety for Health Workers themselves but also communicate the health worker in helping this to happen need for food hygiene to their parents and is to provide both the food handlers and other family members. The earlier that the consumers with information and edu- education in food safety starts, the bet- cation about food safety. ter it is. Even children in kindergartens and nurseries can be trained in some ba- Surveillance sic rules of food hygiene. Teaching chil- Health workers should actively partici- dren about food safety has the doubly pate in the surveillance of foodborne dis- beneficial effect of helping to protect a eases. Epidemiological data are needed vulnerable group and of educating the so that public health authorities can be next generation. aware of the kind of diseases that are In many places, existing school education current in the population, can identify on food safety is limited to teaching which population subgroups are most at about hand-washing after defecation, risk, can plan appropriate food safety pro- protection from flies and rodents, latrine grammes, and can target educational in- use and safe storage of water. Although terventions in an appropriate way. this advice is important, it has not always Surveillance of diseases involves five been enough to prevent foodborne methods: illness, which more often results from insufficient cooking, incorrect storage of n registration of deaths and food, re-use of leftovers, lack of hand- hospital discharge diagnoses; washing prior to food preparation, and n disease notification; other factors that favour contamination, n sentinel surveillance; survival and multiplication of pathogens, or production of toxins in food. n laboratory surveillance; Teachers may themselves have no n outbreak investigation. education in the subject, and may often In most countries, physicians complete a lack teaching materials. Therefore, if death certificate when a person in their teaching about food safety is to be care dies. In many hospitals, and in all improved, teachers should also receive hospitals in some countries, hospital formal training in food safety. Where food records include data on the diagnosis of safety is not on the school curriculum, all patients who are discharged. this presents an opportunity for health workers to visit schools to educate Notification of diseases is often legally children about the importance of food required from physicians or other health hygiene. workers, though this notification may apply only to certain conditions. This Street food vendors and food service information is usually analysed centrally establishments in order to identify trends in health and A substantial amount of food handling illness and also to detect outbreaks of and processing occurs in street food disease. vending operations and food service In sentinel surveillance, selected health establishments. In many situations it is workers or facilities monitor selected not possible to control these operations health events. For foodborne diseases, completely through official inspection. relevant health events might include Control must be exercised by the food syndromes such as diarrhoea, dehydration handlers themselves. The role of the and haemolytic uraemic syndrome, or

73 The role of health workers in food safety

made aware that the health consequences Refugees of foodborne infections may be more When disaster strikes, the safety of the serious for them, and that they may be food supply may be affected, leading to more susceptible than other groups to a greater risk of foodborne disease. At infections such as salmonellosis, the same time, people may flee their enterohaemorrhagic E. coli infection and homes and the situation of refugees and listeriosis. Health workers in contact with displaced persons requires special care the elderly can encourage them to avoid and attention. Conditions in refugee high-risk foods such as meals made from camps are prone to outbreaks of raw or undercooked animal products foodborne disease. Environmental (eggs, meat, milk) or raw seafood. contamination and improper food The sick handling increase the risk of epidemics such as cholera. While education of the Great care should be taken when prepar- public in food safety is important at all ing food for hospital patients — includ- times, in disasters and emergencies it is ing the newborn if they are not breast- an absolute necessity. When there is a risk fed. Food handlers in hospital kitchens of epidemics, families should be should be trained in safe food handling. reminded of the rules of safe food Nurses and dieticians should also receive handling. education in food safety. The highest standards of hygiene will be required for Mass feeding in refugee camps has many foods produced for the sick and elderly. advantages. It ensures, for instance that food is available to everyone. However, It should be remembered that the stand- there are also disadvantages in that it ard of cleanliness and hygienic practice increases the risk of large scale outbreaks in health centres sets an example for visi- of foodborne illness. In refugee centres, tors. A poor standard of hygiene in these food handlers who are responsible for places will have a negative effect while preparing the food, and their supervisors, good hygienic practices will encourage need training in safe food handling and visitors to emulate them. in the HACCP concept. Health workers The undernourished can give them clear instructions about their responsibilities and may even put Undernourished persons are especially up posters with the rules for safe food susceptible to foodborne diseases and handling. Health workers should make should therefore also be seen as an sure that those responsible for the refugee important target group for educational centre understand the important need for interventions. adequate clean water and sanitation, and for proper disposal of unused food and The community other waste. The whole community should participate in health education in food safety. In their Schoolchildren dealings with members of high-risk target Schoolchildren are both a target group for groups and with the community members education on food safety and a channel in general, health workers should ensure for this education as well. Educating that all understand the Ten Golden Rules school children is a very effective strategy for Safe Food Preparation recommended by for preventing foodborne diseases as the WHO. children not only learn about food safety

72 Basic Food Safety for Health Workers how to protect their breast milk from to adopt a critical thought process and chemical or other hazards (e.g. by mini- eventually learn to: mizing contact with pesticides, by avoid- n identify potential hazards and control ing consumption of foods containing measures that are relevant, effective unsafe levels of contaminants). and specific to the operation in ques- Mothers of older infants and young tion and to the work situation; children n prioritize control measures, ensure that While public health authorities have rec- the critical ones are applied correctly ognized the importance of breast-feed- and that they meet the necessary ing in preventing foodborne diseases, al- conditions; and most no attention has been paid to safe n to take appropriate action when food handling during the preparation of conditions are not met. complementary foods. The education of mothers and care-givers in food safety When food handlers lack professional principles is vital if there is to be a training and qualifications, its may be substantial improvement in prevention of difficult to train them in HACCP. In such diarrhoeal diseases in infants and cases, it is nevertheless important to children. In this area, health workers impress on them the value of this clearly have the leading role. Most health technique. Health authorities or health centres already advise mothers on breast- workers could assist in conducting feeding, infant feeding and nutrition, as HACCP studies by identifying hazards, well as other aspects of the care of infants appropriate control measures, critical and children. It would be important that control points, critical limits and these centres extend their information corrective measures and train food and education to include information on handlers in the outcome of the studies. safe food handling practices. WHO has issued a leaflet entitled Basic principles for High-risk groups and people preparation of safe food for infants and young preparing food for them children that health workers can use for advising mothers in food safety. Travellers Travellers will require advice on safe and Professional food handlers unsafe foods in a particular area. If a region has a reputation for unsafe food, Professional food handlers should ideally income from tourism could be affected. receive training and education in two Travellers often consult physicians or aspects of food safety: clinics for vaccination and other a) principles of good hygienic practice; prophylactic or therapeutic treatment. b) application of the HACCP concept Advice on prevailing foodborne diseases to food preparation. and on food and drink likely to be Where food handlers are receiving formal contaminated in certain countries could training and education in food be provided to travellers at vaccination preparation, the above two aspects of centres. WHO has issued a guide on safe food safety should be included in their food for travellers that is intended to help curricula. Training in principles of good meet this need (see bibliography). hygienic practice equip food handlers The elderly with the rudiments of food safety whereas The elderly constitute an increasing pro- training in HACCP helps them to learn portion of the population. They must be

71 The role of health workers in food safety

care-giver who brings a child for treat- Domestic food handlers ment can be given information about how to avoid foodborne hazards by cor- Domestic food handlers are persons who rect food preparation. A group of cases prepare food for consumption by their of diarrhoeal disease would be an oppor- families. Experience has shown that a large tunity to give educational messages to proportion of foodborne disease outbreaks the whole community. In this way the occur in the home as a result of health worker plays not only a reactive mishandling of food. Education of this (curative) role but also a proactive target group will help domestic food (preventive) one. The situation varies handlers to protect themselves and their from country to country and it is not family members. Particular attention possible to prescribe one approach to should be given to WHO’s Ten Golden Rules prevention that will work equally well for Safe Food Preparation (Appendix 2). everywhere. However, some suggestions Expectant mothers are given here that may be adapted to different situations. There are a number of foodborne infections, notably listeriosis and toxoplasmo- Food safety education programmes sis, which may adversely affect the foe- should aim to improve the knowledge tus. Chemical contaminants such as lead and practice of an entire population (in- or methyl mercury, depending on their cluding policy-makers, food producers, level of intake, may also have negative food processors, professional food han- effect on the health of the foetus. Preg- dlers and consumers), as all have a role nant women are often motivated to do to play in food safety. However, certain all they can for the health of their baby. groups, either because of their direct role Health workers — particularly those in in food preparation and/or increased maternal and child health centres and pri- vulnerability to foodborne diseases need mary health care centres — have the re- to receive greater emphasis in the pro- sponsibility of informing women on the gramme. These groups are: type of food/practices which may present greater risks. Education of expectant mothers in food safety should n domestic food handlers who prepare food include information on breast-feeding. A for the family, particularly expectant WHO brochure providing advice on food mothers and mothers with small chil- safety issues of importance to pregnant dren who are especially vulnerable; women is also under preparation. Lactating women n professional food handlers such as street Breast milk is the ideal source of nour- food vendors, catering personnel and ishment and the safest food for infants those working in the food processing during the first 4–6 months of life. It pro- industry (in feeding large numbers of tects them against foodborne diarrhoea people their impact on overall food through its anti-infective properties and safety is considerable); by minimizing exposure to foodborne pathogens. Major efforts are being made at national and international levels to pro- n high-risk groups and people preparing food mote breast-feeding, and a great deal of for them, particularly small children, educational material is available for ad- travellers, pregnant women, the vising mothers on this subject. Health immunocompromised and the elderly. workers can also advise lactating women

70 Basic Food Safety for Health Workers

Chapter 7 The role of health workers in food safety

The first six chapters describe the basics Reliance on treatment, however success- of foodborne illness: what it is, the ful, has its limitations. Treatment of an factors that lead to it, the problems infected individual does not remove the associated with specific foods and food cause of illness from the environment or processing, and how these factors might eliminate behaviours that lead to be controlled. We now consider what the foodborne illness. It does not, therefore, health worker can do to alleviate the prevent other people from becoming ill problem of foodborne illness, particularly by the same route. Nor does infection with regard to children. necessarily confer protection and reduce The health worker has essentially three the risk of a patient succumbing to an- roles: curative, preventive and other episode soon after recovery. So surveillance. while treatment remains an essential task for the health worker, recognition of its limitations has led to greater emphasis being placed on preventive measures to The curative role reduce the overall incidence of illness. In many cases the immediate problem faced by the health worker is how to deal with a sick patient. The foodborne origin The preventive role: of an illness may not be immediately apparent for, although many foodborne controlling foodborne illnesses have diarrhoea as a principal symptom, others can have a variety of hazards presentations. It is not the intention of this book to provide a manual on the The health worker can intervene to treatment of foodborne illness. Much of reduce the incidence of foodborne illness this should already be a key part of a through food safety education health worker’s training and there are a programmes. Cases of diarrhoeal disease, number of other publications that deal for instance, should prompt the health specifically with this aspect (see bibliog- worker to consider whether food is being raphy). prepared correctly. The mother or other

69 Basic Food Safety for Health Workers

References

1 Kilbourne EM. et al. Toxic oil syndrome: a current clinical and epidemiological summary, including comparisons with the eosinophilia-myalgia syndrome. J. Am. Coll. Cardiol., 1991, 18:711–717. 2 Hall RL.The flavour industry. August 1971, p.455 3 Archer D, Young FE. Contemporary issues:diseases with a food vector. Clinical Microbiology Reviews, 1988, 1:377–398. 4. Motarjemi Y. et al. Contaminated weaning food a major risk factor for diarrhoea and associated malnutrition. Bulletin of the WHO, 1993, 71: 79–92. 5. ICMSF. Parasites. In: Micro-organisms in foods, Vol. 5. Microbiological specifications of food pathogens. London, Blackie, 1996, pp. 193–197. 6. Dim LA. et al. Lead and other metals distributed in local cooking salt from the Fofi salt spring in Akwana, Nigeria. J. Environ. Sci. Health, 1991, B26:357–365. 7. Jacopsen JL, Jacopsen SW. Intellectual impairment in children exposed to polychlorinated biphenyls in utero. The New England journal of medicine, 1996, 335: 783–789. 8. Ferrer A, Cabral R. Toxic epidemics caused by alimentary exposure to pesticides: a review. Food additives and contaminants, 1991, 8:755–776. 9. Centers for Disease Control. Lead-contaminated drinking water in bulk-water storage tanks — Arizona and California, 1993. Morbidity and mortality weekly report, 1994, 43:751, 757–758. 10. Coultate TP. Food: the chemistry of its components. Cambridge, Royal Society of Chemistry, 1984, pp. 266– 269. 11. Tylleskär TM et al. Cassava cyanogens and konzo, an upper motorneurone disease found in Africa. Lancet, 339:208–211. 12. Nugon-Baudon L, Rabot S. Glucosinolates and glucosinolate derivatives: implications for protection against chemical carcinogenesis. Nutrition research reviews, 1994, 7: 205–231. 13. Moss MO. Mycotoxins. Mycological research, 1996, 100:513–523. 14. Smith JE, Solomons GL, Lewis CW, Anderson JG. Mycotoxins in human nutrition and health. European Commission CG XII, 1994. 15. Al Bustan MA, Udo EE, Chugh TD. Nasal carriage of enterotoxin producing Staphylococcus aureus among restaurant workers in Kuwait City. Epidemiol. Infect., 1996, 116:319–322. 16. St Louis ME, Peck SHS, Bowering D et al. Annals of internal medicine, 1988, 108:363–368. 17. Lorri W, Svandberg U. Lower prevalence of diarrhoea in young children fed lactic acid fermented cereal gruels. Food nutrition bulletin, 1994, 15:52–63. 18. Blake PA et al. Cholera in Portugal, 1974. American journal of epidemiology, 1997, 105:337–348. 19. Fukjikawa, H. et al. Contamination of microbial foreign bodies in bottled mineral water in Tokyo, Japan. J. Applied Microbiology, 1997, 82:287-291.

75 Bibliography

76 Basic Food Safety for Health Workers

Bibliography

The WHO Ten golden rules for safe food preparation. Geneva, World Health Organization, 1989.

Hygiene in food-service and mass catering establishments. Important rules. Geneva, World Health Organization, 1994 (WHO document WHO/FNU/FOS/94.5).

Food safety measures for eggs & foods containing eggs. Geneva, World Health Organization, 1996 (WHO document WHO/FNU/FOS/96.5).

Basic principles for the preparation of safe food for infants and young children. Geneva, World Health Organization, 1996 (WHO document WHO/FNU/FOS/96.6).

Jacob M. Safe food handling. A training guide for managers of food service establishments. Geneva, World Health Organization, 1989.

Bryan FL. Hazard analysis critical control point evaluations. A guide to identifying hazards and assessing risks associated with food preparation and storage. Geneva, World Health Organization, 1992.

A guide on safe food for travellers. A leaflet that can help travellers avoid illness caused by unsafe food and drink. Geneva, World Health Organiztion, 1994.

Street-vended food: A HACCP-based food safety strategy for governments.Geneva, World Health Organization, 1995 (WHO document WHO/FNU/FOS/95.5)

Food safety. Examples of health education materials. Geneva, World Health Organization, 1989 (WHO document WHO/EHE/FOS/89.2).

The contamination of food. Nairobi, United Nations Environment Programme, 1992. (UNEP/GEMS Environmental Library, No. 5).

Williams T, Moon A, Williams M. Food, environment and health. A guide for primary school teachers. Geneva, World Health Organization, 1990.

Health surveillance and management procedures for food-handling personnel. Report of a WHO Consultation. Geneva, World Health Organization, 1989 (WHO Technical Report Series, No. 785).

Guidelines for cholera control. Geneva, World Health Organization, 1993.

Food technologies and public health. Geneva, World Health Organization, 1995 (WHO document WHO/ FNU/FOS/95.12).

Fermentation: assessment and research. Report of a FAO/WHO Workshop. Geneva, World Health Organization, 1995 (WHO document WHO/FNU/FOS/95.11).

Food irradiation. A technique for preserving and improving the safety of food. Geneva, World Health Organization, 1988.

Training workshop on HACCP. Geneva, World Health Organization, 1996 (WHO document WHO/FNU/ FOS/96.3).

77 Bibliography

International directory of audiovisual material on food safety. Geneva, World Health Organization, 1995 (WHO document WHO/FNU/FOS/95.4).

The role of food safety in health and development. Report of a Joint FAO/WHO Expert Committee on Food Safety, 1984. Geneva, World Health Organization, 1984 (WHO Technical Report Series, No. 705).

Evaluation of programmes to ensure food safety - guiding principles. Geneva, World Health Organization, 1989.

International Conference on Nutrition. A challenge to the food safety community. Geneva, World Health Organization, 1996 (WHO document WHO/FNU/FOS/96.4).

Guidelines for strengthening a national food safety programme. Geneva, World Health Organization, 1996 (WHO document WHO/FNU/96.2).

WHO surveillance programme for control of foodborne infections and intoxications in Europe. Sixth Report (1990- 1992). Geneva, World Health Organization, 1992.

Borgdorff MW, Motarjemi Y. Surveillance of foodborne diseases: what are the options? Geneva, World Health Organization, 1997 (WHO document WHO/FSF/FOS/97.3).

The Treatment of Diarrhoea - A manual for physicians and other senior health workers. Geneva, World Health Organization, 1995 (WHO document WHO/CDR/95).

Advising mothers on management of diarrhoea in the home. Geneva, World Health Organization, 1993 (WHO document WHO/CDD/93.2)

The selection of fluids and food for home therapy to prevent dehydration from diarrhoea. Geneva, World Health Organization, 1995 (WHO document WHO/CDD/93.44)

A healthy pregnancy through a healthy diet. Geneva, World Health Organization (in preparation).

GEMS/FOOD International dietary survey: Infant Exposure to Certain Organochlorine Contaminants from Breast- Milk: a risk assessment. Geneva, World Health Organization, 1998 (WHO document WHO/FSF/FOS/ 98.4).

Other relevant WHO literature on health education

Principles and methods of health education. Report on a WHO Working Group, Dresden, 24-28 October, 1977. Copenhagen, WHO Regional Office for Europe, 1979 (EURO Reports and Studies, No. 11).

Webb JKG. Health education for school-age children. The child-to-child programme. Geneva, World Health Organization 1985.

Dowling MAC, Ritson R. Learning materials for health workers. WHO Chronicle, 1985, 39(5):171–175.

New approaches to health education in primary health care. Report of a WHO Expert Committee. Geneva, World Health Organization, 1983 (WHO Technical Report Series, No. 690).

Research in health education. Report of a WHO Scientific Group. Geneva, World Health Organization, 1969 (WHO Technical Report Series, No. 432).

Teacher preparation for health education. Report of a Joint WHO/UNESCO Expert Committee. Geneva, World Health Organization, 1960 (WHO Technical Report Series, No. 193).

Bury JA et al. Training and research in public health. Policy perspectives for a new public health. Copenhagen, WHO Regional Office for Europe, 1994.

Comprehensive school health education: suggested guidelines for action. Geneva, World Health Organization, 1992.

Abbat FR. Teaching for better learning. A guide for teachers of primary health care staff. 2nd Edition. Geneva, World Health Organization, 1992.

78 Appendix

6. Establish verification procedures Verification includes supplementary tests and procedures which will confirm that the HACCP system is working effectively. It could also indicate that an HACCP plan requires modification.

7. Establish documentation and record keeping This should cover all documentation and records appropriate to the HACCP scheme, such as details of the hazard analysis, CCP and critical limit determination and results from monitoring and verification. Documentation and record keeping should be appropriate to the nature of the operation.

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Appendix 3

The Hazard Analysis and Critical Control Point system (HACCP)1

HACCP is an approach that identifies specific hazards2 and measures for their control. Its full implementation consists of seven principles.

1. Conduct a hazard analysis This identifies and evaluates the potential hazards that may reasonably be expected to occur at each step of food production from growth, harvesting or slaughter, processing and manufacturing, distribution, and preparation through to final consumption. At each stage, the likelihood of occurrence of hazards and the severity of their adverse health effects are assessed, and measures for their control are identified.

2. Determine critical control points These are steps at which control can be applied and is essential to prevent, eliminate or reduce a hazard to an acceptable level.

3. Establish critical limits Critical limits are criteria which separate acceptability from unacceptability. A critical limit may be, for example, a particular temperature, a temperature–time combination, a pH value, or a salt content that is known to control a hazard if it is achieved. For example, a pH of 4.5 or below is known to prevent the growth of Clostridium botulinum, this would therefore be a critical limit that, if achieved, would ensure control of that hazard.

4. Establish monitoring systems An essential part of HACCP is to monitor control parameters (e.g. time-temperature, pH) at critical control points in order to ensure that control of hazards is being exercised and critical limits are observed. In commercial food processing/production this means the introduction of a schedule of testing or observation.

5. Establish corrective actions If monitoring indicates that a critical limit has not been observed, it is necessary to know what action to take to correct the situation and to deal with the food that was produced while the critical control point was not under control. For example, a food might have to be reheated.

1 The description of the HACCP system presented here is based on an adaptation of the Codex Alimentarius Commission’s text on Hazard Analysis and Critical Control Point System and Guidelines for its Application. Codex Alimentarius Commission. Food Hygiene Basic Texts. Rome, Secretariat of the Joint FAO/WHO Food Standards Programme, 1997. 2 A hazard is a biological, chemical or physical agent in, or condition of, food with the potential to cause an adverse health effect. 115 Appendix

6. Avoid contact between raw foods and cooked foods Safely cooked food can become contaminated through even the slightest contact with raw food. This cross- contamination can be direct, as when raw poultry meat comes into contact with cooked foods. It can also be more subtle. For example, don't prepare a raw chicken and then use the same unwashed cutting board and knife to carve the cooked bird. Doing so can reintroduce the disease-causing organisms.

7. Wash hands repeatedly Wash hands thoroughly before you start preparing food and after every interruption — especially if you have to change the baby or have been to the toilet. After preparing raw foods such as fish, meat, or poultry, wash again before you start handling other foods. And if you have an infection on your hand, be sure to bandage or cover it before preparing food. Remember, too, that household pets — dogs, cats, birds, and especially turtles — often harbour dangerous pathogens that can pass from your hands into food.

8. Keep all kitchen surfaces meticulously clean Since foods are so easily contaminated, any surface used for food preparation must be kept absolutely clean. Think of every food scrap, crumb or spot as a potential reservoir of germs. Cloths that come into contact with dishes and utensils should be changed frequently and boiled before re-use. Separate cloths for cleaning the floors also require frequent washing.

9. Protect food from insects, rodents, and other animals Animals frequently carry pathogenic microorganisms which cause foodborne disease. Storing foods in closed containers is your best protection.

10. Use safe water Safe water is just as important for food preparation as for drinking. If you have any doubts about the water supply, boil water before adding it to food or making ice for drinks. Be especially careful with any water used to prepare an infant's meal.

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Appendix 2

WHO’s Ten Golden Rules for Safe Food Preparation

The following rules have been drawn up by WHO to provide guidance on safe food preparation in the home. They should be adapted, as appropriate, to local conditions.

1. Choose foods processed for safety While many foods, such as fruits and vegetables, are best in their natural state, others simply are not safe unless they have been processed. For example, always buy pasteurized as opposed to raw milk and, if you have the choice, select fresh or frozen poultry treated with ionizing radiation. When shopping, keep in mind that food processing was invented to improve safety as well as to prolong shelf-life. Certain foods eaten raw, such as lettuce, need thorough washing.

2. Cook food thoroughly Many raw foods, most notably poultry, meats, eggs and unpasteurized milk, may be contaminated with disease-causing organisms. Thorough cooking will kill the pathogens, but remember that the temperature of all parts of the food must reach at least 70 °C. If cooked chicken is still raw near the bone, put it back in the oven until it's done — all the way through. Frozen meat, fish, and poultry must be thoroughly thawed before cooking.

3. Eat cooked foods immediately When cooked foods cool to room temperature, microbes begin to proliferate. The longer the wait, the greater the risk. To be on the safe side, eat cooked foods just as soon as they come off the heat.

4. Store cooked foods carefully If you must prepare foods in advance or want to keep leftovers, be sure to store them under either hot (near or above 60 °C) or cool (near or below 10 °C) conditions. This rule is of vital importance if you plan to store foods for more than four or five hours. Foods for infants should preferably not be stored at all. A common error, responsible for countless cases of foodborne disease, is putting too large a quantity of warm food in the refrigerator. In an overburdened refrigerator, cooked foods cannot cool to the core as quickly as they must. When the centre of food remains warm (above 10 °C) too long, microbes thrive, quickly proliferating to disease- causing levels.

5. Reheat cooked foods thoroughly This is your best protection against microbes that may have developed during storage (proper storage slows down microbial growth but does not kill the organisms). Once again, thorough reheating means that all parts of the food must reach at least 70 °C.

113 Appendix

Type of illness Paragonimiasis

ICD code ICD-9: 121.2 ICD-10: B66.4 Etiological agent Helminth (trematode/flatworm/lung fluke): Paragonimus westermani (metacercariae). Characteristics of This is a reddish brown hermaphrodite which measures 10–12 mm in length the agent and 5–7 mm in width (adult). The shape varies from linear to spherical. Eggs usually measure 80–120 µm, are golden brown in color, thick-shelled, non- embryonated in faeces or in sputum and have a prominent operculum. The shell is thickened at the abopercular end. Incubation period Acute stage: a few days to several weeks. Chronic stage: pulmonary symptoms begin at around 3 months. Symptoms The early stages are usually asymptomatic. However, heavily infected patients may experience fever, fatigue, generalized myalgia and abdominal pain with eosinophilia. Sequelae Pleuropulmonary paragonimiasis (pulmonary lesion): chronic coughing, thoracic pain, blood-stained viscous sputum. Systemic symptoms of fatigue, fever, myalgia, chest pain and dyspnoea. Severe infections produce tuberculosis-like symptoms. Ectopic paragonimiasis (extrapulmonary lesion): migration of the worm through the brain can cause cerebral haemorrhage, oedema or meningitis. Severe headache, mental confusion, seizure, hemiparesis, hypaesthesia, blurred vision, diplopia, homonymous hemianopsia and meningismus may occur. Abdominal paragonimiasis: results in abdominal pain, and there may be diarrhoea with blood and mucus when the intestinal mucosa is ulcerated. Reservoir/source Fresh-water snails are the first intermediate host; crabs and crayfish are second intermediate hosts. Humans, dogs, pigs and other wild and domestic animals are definitive hosts. Mode of The definitive hosts are infected through consumption of raw, inadequately transmission and cooked or otherwise under-processed freshwater crustaceans (crabs and crayfish) example of foods which contain the metacercariae, or the contamination of other food items, involved in hands and cooking utensils by the metacercariae released from infected crabs outbreaks during food preparation. Following ingestion, the metacercariae (P. westermani) in the infected crustaceans excyst in the duodenum of the host and the larvae penetrate the intestinal wall and migrate beneath the peritoneum where they remain for 5–7 days. Over a period of about 2–3 weeks following infection, the immature worms penetrate the diaphragm, enter the pleural cavity and then move into the lung parenchyma where they mature. At this stage, eggs may be present in the sputum without the host showing any symptoms. During the intial stage of lung infection, the adult worms migrate through the tissues and cause focal haemorrhagic pneumonia. After 12 weeks, the worms in the lung parenchyma typically provoke a granulomatus reaction that gradually proceeds to development of fibrotic encapsulation. Extrapulmonary lesions are caused by worms that reach and develop in ectopic foci. Specific control Industrial: safe disposal of excreta and sewage/wastewater to prevent measures contamination of rivers. Food service establishment/household: thorough cooking of food, i.e. crabs and crayfish, and hygienic handling of these foods. Consumers should avoid consumption of raw or undercooked or under- processed crabs and crayfish. Others: control of snails with molluscicides where feasible; drug treatment of the population to reduce the reservoir of infection; elimination of stray dogs and cats. Occurrence Africa, e.g. Cameroon, Nigeria; Americas, e.g. Ecuador, Peru; Asia, e.g. China, Japan, Lao People’s Democratic Republic, Philippines, Republic of Korea, Thailand. Estimated rate of occurrence in these countries is +++.

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Type of illness Opisthorchiasis

ICD code ICD-9: 121.0 ICD-10: B66.0 Etiological agent Helminth (trematode/flatworm/liver fluke): Opisthorchis viverrini and Opisthorchis felineus. Characteristics Morphological features resemble that of Clonorchis sinensis. The worm lives in of the agent the intrahepatic bile ducts and pancreas and has been also found in the lungs. It measures 8–11 mm x 1.5–2 mm. Eggs measure 30 µm x 12 µm and are slenderer than the C. sinensis eggs. Incubation period Opisthorchis felineus: 2–4 weeks, very occasionally 1 week. Symptoms Fever, abdominal pain, dizziness, urticaria. Chronic cases may lead to diarrhoea, flatulence, fatty food intolerance, epigastric and right upper quadrant pain, jaundice, fever, hepatomegaly, lassitude, anorexia, and in some cases emaciation and oedema. Sequelae Cholecystitis, cholangitis, liver abscess and gallstones. Cholangiocarcinoma is associated with O. viverrini infection and perhaps also with O. felineus. Reservoir/source The first intermediate host is the freshwater snail; several fish species act as second intermediate host. Humans, dogs, cats, and other mammals that eat fish or fish waste are definitive hosts. Mode of Humans are infected by consumption of raw or under-processed freshwater transmission and fish. example of foods The life cycle of Opisthorchis is similar to that of C. sinesis. involved in outbreaks Specific control Industrial: safe disposal of excreta and sewage/wastewater; treatment of measures wastewater used for aquaculture; irradiation of freshwater fish; freezing; heat treatment e.g. canning. Food service establishment/household: thorough cooking of freshwater fish. Consumers should avoid consumption of raw or undercooked freshwater fish. Others control of snails with molluscicides where feasible; drug treatment of the population to reduce the reservoir of infection; elimination of stray dogs and cats. Occurrence Opisthorchis viverrini: Cambodia, Lao Peoples Democratic Republic, Thailand. Opisthorchis felineus: Europe: Baltic states, eastern Germany, Kazakhstan, Poland, the Russian Federation, Ukraine; Asia: India. Japan, Thailand. In European countries the estimated rate of occurrence is ++ and in Asian countries, the estimated rate of occurrence is +++.

111 Appendix

Type of illness Fascioliasis

ICD code ICD-9: 121.3 ICD-10: B66.3 Etiological agent Helminth (trematode/flatworm/liver fluke): Fasciola hepatica and Fasciola gigantica. Characteristics of Fasciola hepatica: large fluke (23–30 mm x15 mm), pale grey in colour with dark the agent borders, leaf-shaped with a distinct cephalic cone at the anterior end. Eggs are usually 130–150 µm x 63–90 µm. They have an inconspicuous operculum, are non-embryonated, and often have a shell irregularity at the abopercular end. Fasciola gigantica is bigger and may attein a length of 75 mm. Incubation period 4–6 weeks. Symptoms Fever, sweating, abdominal pain, dizziness, cough, bronchial asthma, urticaria. In children, the acute infection is accompanied by severe clinical manifestations, including right upper quadrant pain or generalized abdominal pain, fever and anaemia, and can be fatal. Ectopic infections are common in man. Sequelae Necrotic lesions, inflammatory, adenomatous and fibrotic changes in the bile duct, biliary stasis, atrophy of the liver and periportal cirrhosis, cholecystitis and cholelithiasis. Reservoir/source Snails are the intermediate host; sheep, cattle and humans are the definitive host. Mode of Infection in human is associated with the consumption of uncultivated raw transmission and watercress (Nasturtium officinale) and other salad plants, such as dandelions, example of foods bearing metacercariae. involved in After ingestion, the larvae are released from the cyst envelopes into the outbreaks duodenum, pass through the intestinal wall to the abdominal cavity, enter the liver and after development enter the bile ducts and begin laying non- embryonated eggs 3–4 months after initial exposure. The eggs are carried by the bile into the intestine, and evacuated with the faeces. The eggs mature and the miracidia emerge from the eggs to the water in a few weeks. The miracidia penetrate the snail (intermediate host), and turn into sporocysts and in about 3 weeks produce rediae which, in turn, produce cercariae. The cercariae may begin to emerge from the snails in six weeks under favourable conditions. After leaving the snail, the cercariae swim in the water and cyst on vegetation, turning into metacercariae which can survive for a long time in a wet environment. The life cycle is then complete. Specific control Industrial: safe disposal of excreta and sewage/wastewater; drug treatment of measures livestock against the parasite; prevention of animal access to commercial watercress beds and control of water used to irrigate the beds. Food service establishment/household: thorough cooking of food. Consumers should avoid consumption of raw watercress. Others: control of snails with molluscicides where feasible; drug treatment of the population to reduce the reservoir of infection. Occurrence Africa, e.g. Egypt, Ethiopia; Americas, e.g. Bolivia, Ecuador, Peru; Asia, e.g. China; Islamic Republic of Iran; Europe: France, Portugal, Spain. The estimated rate of occurrence varies, depending on the country, from ++ to +++.

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Type of illness Clonorchiasis

ICD code ICD-9: 121.1 ICD-10: B66.1 Etiological agent Helminth (trematode/flatworm): Clonorchis sinensis, also known as Chinese or oriental liver fluke. Characteristics of This is a flattened worm, 10–25 mm long, 3–5 mm wide and usually spatula the agent shaped. It is yellow-brown, owing to bile staining; has an oral and a ventral sucker and is a hermaphrodite. Eggs measure 20–30 µm x 15–17 µm; they are operculate and one of the smallest trematode eggs to occur in man. Incubation period Unpredictable: varies with the number of worms present. Symptoms begin with the entry of immature flukes into the biliary system, within one month after encysted larvae (metacercarie) are ingested. Symptoms Gradual onset of discomfort in the right upper quadrant, anorexia, indigestion, abdominal pain or distension and irregular bowel movement. Patients who are heavily infected experience weakness, weight loss, epigastric discomfort, abdominal fullness, diarrhoea, anaemia, oedema. In the later stages, jaundice, portal hypertension, ascites and upper gastointestinal bleeding occur. Sequelae The liver (predominantly the left lobe) is enlarged. The spleen can be palpated in only a small percentage of infected cases. Recurrent pyogenic cholangitis is a serious complication of clonorchiasis. The pancreas may be involved in severe cases of C. sinensis infection. The pathology of pancreatic clonorchiasis is similar to that of hepatic lesion, namely adenomatous hyperplasia of the ductal epithelium. When acute pancreatitis occurs, inflammation is present. Cholangiocarcinoma is also associated with clonorchiasis. Repeated or heavy infection during childhood has been reported to cause dwarfism with retarded sexual development. Reservoir/source Snails are the first intermediate host. Some 40 species of river fish serve as the second intermediate host. Humans, dogs, cats and many other species of fish- eating mammals are definitive hosts. Mode of People are infected by eating raw or under-processed freshwater fish containing transmission and encysted larvae (metacercariae). During digestion, the larvae are freed from the example of foods cysts and migrate via the common bile duct to biliary radicles. Eggs deposited involved in in the bile passages are evacuated in faeces. Eggs in faeces contain fully developed outbreaks miracidia; when ingested by a susceptible operculate snail, they hatch in its intestine, penetrate the tissues and asexually generate larvae (cercariae) that migrate into the water. On contact with a second intermediate host, the cercariae penetrate the host and encyst, usually in muscle, occasionally on the underside of scales. The complete life cycle from person to snail to fish to person requires at least 3 months. Specific control Industrial: Safe disposal of excreta and sewage/wastewater to prevent measures contamination of rivers; treatment of wastewater used for aquaculture; irradiation of freshwater fish; freezing; heat treatment, e.g. canning. Food service establishment/household: thorough cooking of freshwater fish. Consumers should avoid consumption of raw or undercooked freshwater fish. Other: control of snails with molluscicides where feasible; drug treatment of the population to reduce the reservoir of infection; elimination of stray dogs and cats. Occurrence Endemic in Western Pacific areas: China, Hong Kong, Japan, Malaysia, Republic of Korea, Singapore, Thailand,Viet Nam. Estimated rate of occurrence: ++/+++. In Europe: eastern part of Russian Federation (Estimated rate of occurrence: ++). Other comments About one-third of chronic infections are asymptomatic.

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Type of illness Taeniasis: Taenia solium taeniasis and cysticercosis Taenia saginata taeniasis

ICD code ICD-9: 123.0 (Taenia solium taeniasis); 123.2 (Taenia saginata taeniasis); 123.1 (cysticercosis) ICD-10: B68.0 (Taenia solium taeniasis); B68.1 (Taenia saginata taeniasis), B69 (cysticercosis) Etiological agent Helminth (cestode/tapeworm): Taenia solium and Cysticercus cellulosae (larvae of T. solium) and Taenia saginata and Cysticercus bovis (larvae of T. saginata). Characteristics of T. solium causes both intestinal infection with adult worms as well as somatic the agent infection with the eggs. The adult worm comprises a scolex 1 mm in diameter, armed with two rows of hooks and four suckers. The strobila ranges in length from 1.8–4 m. T. saginata causes only intestinal infection with adult worms. The adult worm comprises a scolex 1–2 mm in diameter, equipped with four suckers, a neck, and a strobila that ranges in length from 35 mm to 6 m. Incubation period Symptoms of cysticercosis appear from a few days to over 10 years. Eggs appear in the stools 8–12 weeks after infection with T. solium, and 10–14 weeks after infection with T. saginata. Symptoms Nervousness, insomnia, anorexia, weight loss, abdominal pain and digestive disturbance. Cysticercosis may cause epileptiform seizures, signs of intracranial hypertension or psychiatric disturbance. Cysticercosis may be fatal. Sequelae Cysticercosis may affect the central nervous system. When eggs or proglottides of T. solium are swallowed, the eggs hatch in the small intestine and the larvae migrate to subcutaneous tissue, striated muscles, and other tissues and vital organs of the body where they form cysts. Severe health consequences occur when the larvae localize in the eye, central nervous system or heart. Reservoir/source Humans; pigs and cattle are the intermediate host for T. solium and T. saginata. Mode of Taeniasis is caused by consumption of raw or undercooked beef (Taenia transmission and saginata) or pork ( Taenia solium) containing cysticerci. example of foods Gravid proglottides of the parasite are excreted in faeces. Eggs within the involved in segments are infective. Cattle ingest the eggs deposited on pasture and pigs outbreaks ingest those deposited on soil. When viable eggs are ingested by cattle or pigs they develop into cysticerci in the muscle. Cysticercosis is caused by ingestion of T. solium eggs by the faecal–oral route, person-to-person contact, autoinfection (unwashed hands) or consumption of contaminated food e.g. vegetables. Specific control Industrial: prevention of faecal contamination of soil, water, human and animal measures food through safe disposal of sewage; avoidance of sewage water for irrigation use. Irradiation, heat treatment, and freezing kills the cysticerci. Food service establishment/household: thorough cooking of meat. Other: early diagnosis and treatment to prevent cysticercosis. Occurrence Worldwide. Most common in Africa, Latin America, eastern Europe, and south- east Asia. Estimated rate of occurrence varies from + to ++ in high prevalence areas. Other comments T. saginata eggs are infective only in cattle, T. solium eggs are infective in pigs and humans. Eggs of both species are disseminated in the environment as long as the worm remains in the intestine, sometimes for more than 30 years; eggs may remain viable in the environment for months.

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Type of illness Trichinellosis (trichiniasis, trichinosis)

ICD code ICD-9: 124 ICD-10: B75 Etiological agent Helminth (nematode/roundworm): Trichinella spiralis (larvae in infected muscle). Characteristics of White intestinal worm, visible to the naked eye. The transmissible form of this the agent parasite is a larval cyst approximately 0.4 mm x 0.25 mm which occurs in pork muscle. In the initial phase of trichinellosis, the larvae ingested with the meat develop rapidly into adults in the epithelium of the intestine. Female worms produce larvae which penetrate the lymphatics or venules and are disseminated via the blood throughout the body. The larvae become encapsulated in the skeletal muscle. Incubation period Initial phase: a few days. Systemic symptoms: 8–21days. Symptoms Symptoms range from inapparent infection to fulminating and fatal disease, depending on the number of larvae ingested. Symptoms during the initial invasion are nausea, vomiting, diarrhoea and fever. During the phase of parasite dissemination to the tissues, there may be rheumatic manifestations, muscle soreness and pain together with oedema of the upper eyelids, sometimes followed by subconjunctival, subungual and retinal haemorrhages, pain and photophobia. Thirst, profuse sweating, chills, weakness, prostration and rapidly increasing eosinophilia may follow shortly after the ocular symptoms. Sequelae Cardiac and neurological complications may appear in weeks 3–6; in the most severe cases death due to myocardial failure may occur. Duration 2 weeks to 2–3 months. Reservoir/source Pigs, dogs, cats, rats, horses and other mammals of man’s domestic environment. Mode of Ingestion of raw or undercooked meat (pork, horse) containing the encysted transmission and larvae. example of foods Examples of foods involved include pork, horse, wild boar, game. involved in outbreaks Specific control Industrial: irradiation of meat, freezing, heating and curing. measures Food service establishment/household: thorough cooking of meat, freezing (minus 15 °C for 30 days). Additionally, hunters should thoroughly cook all game. Occurrence Worldwide, with predominance in countries where pork or game is eaten. Estimated rate of occurrence varies from + to ++ in high prevalence areas.

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Type of illness Ascariasis

ICD code ICD-9: 127.0 ICD-10: B77 Etiological agent Helminth (nematode/roundworm): Ascaris lumbricoides (egg with infective larva). Characteristics of Ascaris lumbricoides is a large roundworm infecting the small intestine. Adult the agent males are 15–31cm x 2–4 mm and females are 20– 40cm x 3–6mm. Eggs undergo embryonation in the soil; after 2–3 weeks at warm temperature they become infective and may remain viable for several months or even years in favourable soils. The larvae emerge from the egg in the duodenum, penetrate the intestinal wall and reach the heart and the lungs in the blood. Larvae grow and develop in the lungs; 9–10 days after infection they break out of the pulmonary capillaries into the alveoli and migrate through the bronchial tubes and trachea of the pharynx where they are swallowed and reach the intestine 14–20 days after infection. In the intestine they develop into adults and begin laying eggs 40–60 days after ingestion of the embryonated eggs. The life cycle is complete after 8 weeks. Incubation period First appearance of eggs in stools is 60–70 days. In larval ascariasis, symptoms occur 4–16 days after infection. Symptoms Gastrointestinal discomfort, colic and vomiting, fever; observation of live worms in stools. Some patients may have pulmonary symptoms or neurological disorders during migration of the larvae. However there are generally few or no symptoms. Sequelae A heavy worm infestation may cause nutritional deficiency; other complications, sometimes fatal, include obstruction of the bowel by a bolus of worms (observed particularly in children), obstruction of bile or pancreatic duct. Reservoir/source Humans; soil and vegetation on which faecal matter containing eggs has been deposited. Mode of Ingestion of infective eggs from soil contaminated with human faeces or transmission and contaminated vegetables and water. example of foods involved in outbreaks Specific control Use of toilet facilities; safe excreta disposal; protection of food from dirt and measures soil; thorough washing of produce. Food dropped on the floor should not be eaten without washing or cooking, particularly in endemic areas. Occurrence Worldwide. There is a high prevalence (exceeding 50%) in moist and tropical countries. Estimated rate of occurrence: + to +++ depending on the region. Other comments In endemic areas the highest prevalence is among children aged 3–8 years.

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Type of illness Anisakiasis

ICD code ICD-9: 127.1 ICD-10: B81.0 Etiological agent Helminth (nematode/roundworm): Anisakis spp. (larval stage). Characteristics of Slender, threadlike parasite measuring 1.5–1.6 cm in length and 0.1 cm in the agent diameter. Incubation period A few hours; symptoms related to the intestine a few days or weeks. Symptoms The motile larvae burrow into the stomach wall producing acute ulceration and nausea, vomiting and epigastric pain, sometimes with haematemesis. They migrate upward and attach themselves to the oropharynx causing coughing. In the small intestine they cause eosinophilic abscesses. Reservoir/source Sea mammals (for Anisakis spp. that are parasitic to man). Mode of Consumption of the muscles of some saltwater fish which has been inadequately transmission and processed. example of foods Examples of foods involved include raw fish dishes (e.g sushi, sashimi, herring, involved in cebiche). outbreaks Specific control Industrial: irradiation; heat treatment, freezing, candling, cleaning (evisceration) measures of fish as soon as possible after they are caught (will prevent post-mortem migration of infective larvae from the mesenteries of the fish to muscles). Food service establishment/household: cleaning of fish; thorough cooking before consumption; freezing (minus 20°C for 7 days). Occurrence Mainly in countries where consumption of raw or inadequately processed fish is common, e.g. Northern Europe, Japan, Latin America. Over 12 000 cases have been reported in Japan. Cases have also been reported in other parts of the world as eating habits change with immigration. Other comments Symptoms mimic those of appendicitis.

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Type of illness Toxoplasmosis and congenital toxoplasmosis

ICD code ICD-9: 130 and 771.2 ICD-10: B58 and P 37.1 Etiological agent Protozoa: Toxoplasma gondii (belonging to the family Sarcocystidae). Characteristics of A coccidian protozoan; infections are often asymptomatic. the agent Incubation period 5–23 days. Symptoms Infections are often asymptomatic or present an acute disease with lymphadenopathy and lymphocytosis persisting for days or weeks. Sequelae During pregnancy transplacental infection may cause abortion or stillbirth, chorioretinitis, brain damage. In immunocompromised individuals it may cause cerebritis, chorioretinitis, pneumonia, myocarditis, rash and/or death. Cerebral toxoplasmosis is a particular threat for AIDS patients. Reservoir/source Cats and other felines; intermediate hosts are sheep, goats, rodents, pigs, cattle and birds, all of which may carry an infective stage of T. gondii, encysted in tissue e.g. muscle or brain, which remains viable for long periods, perhaps the entire life of the animal. Mode of Infections occur through ingestion of oocysts. Children may acquire the infection transmission and by playing in sand polluted with cat excreta. Oocysts shed by cats can sporulate example of foods and become infective 1–5 days later and may remain infective in water or soil for involved in a year. Infection may also be acquired by eating raw or undercooked meat outbreaks containing the cysts or food and water contaminated with feline faeces. Transplacental infection may also occur when the infection is acquired during pregnancy. Examples of foods involved include raw or undercooked meat, vegetables and goat’s milk. Specific control Industrial: irradiation of meat. measures Food service establishments, household: thorough cooking of meat; careful washing of fruits and vegetables; good personal hygiene — particularly after contact with cats and before food preparation; safe disposal of cat faeces. Consumers: particularly, pregnant women if not immune, should be advised to avoid raw or undercooked meat; wash vegetables carefully and wash hands after contact with cats. Occurrence Worldwide. Estimated rate of occurrence: + to ++. Other comments T. gondii cysts remain in the tissue and may reactivate if the immune system becomes compromised, e.g. by cytotoxic or immunosuppressive therapy or in patients with AIDS. In these groups the infection may be fulminant and fatal.

104 Basic Food Safety for Health Workers

Type of illness Giardiasis

ICD code ICD-9: 007.1 ICD-10: A.07.1 Etiological agent Protozoa: Giardia lamblia. Characteristics of This flagellate protozoan has an environmentally resistant cyst stage as well as the agent the vegetative trophozoite stage. Cysts are oval and 7–14 m long. They are resistant to the chlorination process used in most water-treatment systems but are killed by conventional cooking procedures. Incubation period 4–25 days, usually 7–10 days. Symptoms Once ingested, the cysts release the active trophozoite which adheres to the gut wall. Illness is characterized by diarrhoea (which may be chronic and relapsing), abdominal cramps, fatigue, weight loss, anorexia and nausea. It is thought that the symptoms may be caused by a protein toxin. Sequelae Cholangitis, dystrophy, joint symptoms, lymphoid hyperplasia. Duration Weeks–years. Reservoir/source Humans and animals. Mode of Giardia cysts are excreted in large numbers by an infected individual. Illness is transmission and spread through the faecal–oral route, person-to-person contact or faecally example of foods contaminated food and water. Cysts have been isolated from lettuces and fruit involved in such as strawberries. The infection is also associated with drinking-water outbreaks from surface waters and shallow wells. Examples of foods involved include: water, home-canned salmon and noodle salad. Specific control Industrial: filtration and disinfection of water supply; sanitary disposal of excreta, measures sewage water, treatment of irrigation water. Food service establishment/household: boiling of water, when safe water is not available; thorough washing of fruit and vegetables; thorough cooking of foods; good hand hygiene. Consumers: and more specifically campers, should avoid drinking surface water unless it has been boiled or filtered. Occurrence Worldwide. In industrialized countries, the estimated rate of occurrence is ++ and in developing countries with poor sanitation +++. Other comments Number of asymptomatic carriers is high. Children are affected more frequently than adults. Illness is prolonged and more serious in the immunocompromised, particularly AIDS patients. Tourists are particularly at risk.

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Type of illness Cryptosporidiosis

ICD code ICD-9: 136.8 ICD-10: A07.2 Etiological agent Protozoa: Cryptosporidium parvum. Characteristics of The organism has a complex life cycle that can take place in a single human or the agent animal host. It produces resistant oocysts typically 4–6 m. which are very resistant to the chlorination process, but are killed by conventional cooking procedures. Incubation period 2–14 days. Symptoms Diarrhoea (persistent diarrhoea), nausea, vomiting and abdominal pain sometimes accompanied by an influenza-like illness and fever. Sequelae Illness is more serious in the immunocompromised, particularly AIDS patients, and leads to severe nutrient malabsorption and weight loss. Duration A few days up to 3 weeks. Reservoir/source Humans and wild and domestic animals, e.g. cattle. Mode of Spread through the faecal–oral route, person-to-person contact, or consumption transmission and of faecally contaminated food and water. Other routes of transmission include example of foods bathing in contaminated swimming pools. involved in Examples of foods involved include raw milk, drinking-water and apple cider. outbreaks Specific control Industrial: pasteurization/sterilization of milk, filtration and disinfection of measures water, sanitary disposal of excreta, sewage and wastewater. Food service establishment/household: boiling of water when safe water is not available; boiling of milk; thorough cooking of food; good hand hygiene. Occurrence Worldwide. Cryptosporidiosis is one of the leading causes of diarrhoeal disease in infants and young children. It constitute 5–15 % of diarrhoeal disease cases in children seen at treatment centres. The estimated rate of occurrence is +++. In industrialized countries, it occurs often in day-care centres. Estimated rate of occurrence: ++. Other comments Children under the age of 5 years are more at risk. Immunocompromised individuals, e.g. AIDS patients, may suffer from longer and more severe infection. In AIDS patients, infection may lead to death.

102 Basic Food Safety for Health Workers

Type of illness Amoebiasis (amoebic dysentery)

ICD code ICD-9: 006 ICD-10: A06 Etiological agent Protozoa: Entamoeba histolytica. Characteristics of An amoeboid protozoan that is an aerotolerant anaerobe. It survives in the the agent environment in an encysted form. Cysts remain viable and infective for several days in faeces and may survive in soil for at least 8 days at 28 –34 °C, and for more than 1 month at 10 °C. Relatively resistant to chlorine. Incubation period 2–4 weeks, but may range from a few days to several months. Symptoms Severe bloody diarrhoea, stomach pains, fever and vomiting. Most infections remains symptomless. Sequelae Liver abscess. Duration Weeks–months. Reservoir/source Mainly humans, but also dogs and rats. The organism is also found in nightsoil, and sewage irrigation. Mode of Transmission occurs mainly through the ingestion of faecally contaminated transmission and food and water containing cysts. Cysts are excreted in large numbers (up to 5 x example of foods 107 cysts per day) by an infected individual. Illness is spread by the faecal–oral involved in route, person-to- person contact or faecally contaminated food and water. outbreaks Examples of foods involved include fruit and vegetables, and drinking-water. Specific control Industrial: filtration and disinfection of water supply; hygienic disposal of measures sewage water, treatment of irrigation water. Food service establishment/household: boiling of water, when safe water is not available; thorough washing of fruit and vegetables; thorough cooking of food; good hand hygiene. Occurrence Worldwide, particularly in young adults. Estimated rate of occucrrence: very low in industrialized countries: + and very frequent in developing countries with poor sanitation: ++.

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Type of illness Viral hepatitis A

ICD code ICD-9: 070.1 ICD-10: B15 Etiological agent Virus: Hepatitis A virus; member of Picornaviridae. Characteristics Small round virus, around 28 nm in diameter, containing single-stranded RNA. of the agent The virus multiplies in the gut epithelium before being carried by the blood to the liver. In the later part of incubation, the virus is shed in the faeces. Relatively acid-resistant. Incubation period 2–6 weeks; usually about 25 days. Symptoms Early symptoms are loss of appetite, fever, malaise, abdominal discomfort, nausea and vomiting. These are followed by symptoms of liver damage such as passage of dark urine, pale stools and jaundice. Sequelae Liver disorders, particularly in older persons. Duration Varies in clinical severity: mild, with recovery within few weeks, to severe, lasting several months. Reservoir/source Humans: sewage and contaminated water. Mode of Spread through the faecal–oral route, primarily person-to-person. It can also transmission and be transmitted through food and water as a result of sewage contamination or example of foods infected food handlers. involved in Risk of transmission is greatest during the second half of the incubation outbreaks period until a few days after the appearance of jaundice. Examples of foods involved include: Shellfish, raw fruit and vegetables, bakery products. Specific control Industrial: treatment of water supply, safe sewage disposal. measures Food service establishment/household: good personal hygiene, in particular, thorough hand-washing with soap and water before handling foods and abstinence from handling food when infected; thorough cooking of shellfish. An effective vaccine is available, and vaccination of professional food handlers and travellers should be considered. Occurrence Worldwide. Estimated rate of occurrence:++. Other comments There may be asymptomatic carriers. Infection in adults is most severe. In children it is often asymptomatic and confers immunity. Case–fatality rate is low, about 0.3%. A higher case–fatality rate may occur in adults over 50 years of age.

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Type of illness Viral gastroenteritis

ICD code ICD-9: 008.8 ICD-10: A08 Etiological agent Virus: a number of different viruses have been established as causes of gastroenteritis. These include adenoviruses, coronaviruses, rotaviruses, parvoviruses, caliciviruses and astroviruses. Those most commonly associated with foodborne outbreaks are described as small, round-structured viruses (SRSVs), which include Norwalk agent. Characteristics These viruses exhibit a range of biochemical and physical characteristics. of the agent Incubation period 15–50 hours. Symptoms Diarrhoea and vomiting which is often severe and projectile with sudden onset. Duration 2 days. Reservoir/source Humans. Mode of Gastroenteritis viruses are usually spread by the faecal–oral route. Food and transmission and drinking-water may be contaminated either at source when exposed to sewage/ example of foods wastewater in the environment or used for irrigation, or by an infected food involved in handler. Filter-feeding shellfish are the most common food contaminated at outbreaks source, but a far wider range of different cooked and uncooked foods have been implicated in secondary contamination by food handlers. Specific control Hygienic sewage disposal, treatment of drinking-water, treatment of measures wastewater used for irrigation. Good personal hygiene (i.e. hand hygiene); abstinence from handling food when ill, especially when diarrhoea is present. Occurrence Worldwide. Estimated rate of occurrence for Rotavirus: ++/+++; and for other viral infections: +. Rotavirus infections constitute 15–25% of diarrhoeal disease cases identified in children seen at treatment centres in the developing countries.

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Type of illness Poliomyelitis

ICD code ICD-9: 045 ICD-10: A80 Etiological agent Virus: Poliovirus; member of Picornaviridae. Characteristics of Small round virus, which contains single- stranded RNA and can withstand the agent acidity in the range of pH 3–5. The poliovirus infects the gastrointestinal tract and spreads to the regional nodes, and, in a minority of cases, to the nervous system. Incubation period 3–14 days. Symptoms Poliomyelitis may be a transient viraemia characterized by fever and malaise. In a minority of cases, it may progress to a second stage of persistent viraemia where the virus invades the central nervous system causing varying degrees of paralysis and in some cases even death. Severe muscle pain and stiffness of the neck and back with or without flaccid paralysis are symptoms of the more severe illness. Flaccid paralysis occurs in less than 1% of poliovirus infections. Most often paralysis is in the legs, sometimes in the arms. Paralysis of the muscles used in respiration and/or swallowing is life threatening. The infection in young children is usually asymptomatic and confers immunity, but is more severe in older children and young adults. Sequelae Permanent paralysis. Reservoir/source Humans; most frequently people with no apparent symptoms of infection. Mode of Principally person-to-person, through the faecal–oral route. Food and drinking- transmission and water are potential modes of transmission where hygiene standards are low. In example of foods some instances, milk and other foodstuffs contaminated with faeces have been involved in a vehicle for transmission. outbreaks Specific control Vaccination. measures Specific control measures with regard to food include: Industrial: treatment of drinking-water, and an effective sewage disposal system. Food service establishment/household: safe food preparation practices including careful hand-washing with soap and water, thorough cooking and reheating of food prior to consumption and thorough washing of all fruit and vegetables. Occurrence Poliomyelitis has been almost entirely eradicated in industrialized countries and the Americas owing to effective immunization. It occurs in developing countries with an estimated rate of occurrence varying from + to ++, depending on immunization programmes. Other comments During the few days prior to, and following the onset of symptoms, the risk of transmission is greatest. Infants and children under 5 years of age are the most frequently affected. Immunization of the elderly is recommended, particularly when travelling abroad.

98 Basic Food Safety for Health Workers

Type of illness Yersiniosis

ICD code ICD-9: 027.8 ICD-10: A04.6 Etiological agent Bacteria: Yersinia enterocolitica Characteristics of Gram-negative, facultatively anaerobic, motile, non-spore-forming rods of the the agent family Enterobacteriaceae. Y. enterocolitica is a psychrotroph capable of growing at temperatures between 0 °C and 44 °C, but optimally at 29 °C. Growth will occur in a pH range of 4.6–9.0, but optimally at pH 7–8. It will grow in media containing 5% salt but not 7% salt. Incubation period 1–11 days (but usually 24–36 hours). Symptoms Abdominal pain, diarrhoea accompanied by a mild fever, and sometimes vomiting. Sequelae Sequelae are observed in 2–3% of cases: reactive arthritis, Reiter disease, eye complaints, cholangitis, erythema nodosum, septicaemia, hepatic and splenic abscesses, lymphadenitis, pneumonia, spondylitis. Duration Symptoms usually abate after 2–3 days; although they may continue in a milder form for 1–3 weeks. Reservoir/source A variety of animals, but pathogenic strains are most frequently isolated from pigs. Mode of Illness is transmitted through consumption of pork products (tongue, tonsils, transmission and gut), cured or uncured, as well as milk and milk products. example of foods involved in outbreaks Specific control Food service establishment/household: thorough cooking of pork products, and measures prevention of cross-contamination. Occurrence Northern Europe and Australia: estimated rate of occurrence: +/++; USA: estimated rate of occurrence: +. Other comments Untreated cases continue to excrete the organism for 2–3 months. The disease is often misdiagnosed as appendicitis. Case–fatality rate is 0.03%.

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Type of illness Vibrio vulnificus infection

ICD code ICD-9: 005.8 ICD-10: A05.8 Etiological agent Bacteria: Vibrio vulnificus. Characteristics of Gram-negative, non-spore-forming rods. Optimal temperature for growth is the agent 37 °C. Incubation period 12 hours–3 days. Symptoms Profuse diarrhoea with blood in stools; the organism is associated with wound infections and septicaemia which may originate from the gastrointestinal tract, or traumatized epithelial surfaces. Sequelae Produces septicaemia in persons with chronic liver diseases, chronic alcoholism, haemochromatosis, or those who are immunodepressed. Over 50% of patients with primary septicaemia may die; the fatality rate increases to 90% in hypotensive individuals. Duration Days–weeks. Reservoir/source Natural habitat is coastal or estuarine waters. Mode of All known cases are associated with seafood, particularly raw oysters. transmission and example of foods involved in outbreaks Specific control Consumers, particularly vulnerable groups including the elderly, those with measures underlying liver disease or immunodepressed through treatment or disease, and alcoholics, should not eat raw seafood. Occurrence Frequently in Europe,USA and the Western Pacific Region. Estimated rate of occurrence: +/++. Other comments Case–fatality rate can be as high as 40–60% .

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Type of illness Vibrio parahaemolyticus gastroenteritis

ICD code ICD-9: 005.4 ICD-10: A.05.3 Etiological agent Bacteria: Vibrio parahaemolyticus Characteristics of Basic characteristics are the same as for V. cholerae. V. parahaemolyticus differs in the agent that it is halophilic and will grow at salt levels up to 8% and with a minimum

aw of 0.94. Growth is optimal and very fast at 37 °C (doubling time about 10 minutes) and will occur down to around 10 °C. V. parahaemolyticus is more sensitive to extremes of temperature than V. cholerae and will die at chill temperatures. Incubation period Often 9–25 hours, up to 3 days Symptoms Profuse watery diarrhoea free from blood or mucus, abdominal pain, vomiting, and fever. A dysenteric syndrome has been reported from some countries, particularly Japan. Sequelae Septicaemia. Duration Up to 8 days. Reservoir/source Natural habitat is coastal seawater and estuarine brackish waters above 15 °C and marine fish and shellfish. Mode of Mainly consumption of raw or undercooked fish and fishery products, or transmission and cooked foods subject to cross-contamination from raw fish. example of foods involved in outbreaks Specific control Food service establishment/household: thorough heat treatment of seafood; rapid measures chilling; prevention of cross-contamination from raw seafood products to other foods or preparation surfaces. Occurrence The illness has been reported primarily in countries in the western Pacific region and in particular Japan as well as south-east Asia and the USA. Estimated rate of occurrence: +/++. Other comments Case–fatality rate in industrialized countries is less than 1%.

95 Appendix

Type of illness Typhoid and paratyphoid fevers

ICD code ICD-9: 002.0 and 002.1–002.9 ICD-10: A01.0 and A01.1–A01.4 Etiological agent Bacteria: Salmonella Typhi and Salmonella Paratyphi types A–C. Characteristics of As for non-typhoid salmonellae, except minimum growth pH is higher (4.9). the agent Incubation period 10–20 days with a range of 3 days to 8 weeks. Symptoms Systemic infections characterized by high fever, abdominal pains, headache, vomiting, diarrhoea followed by constipation, rashes and other symptoms of generalized infection. Sequelae Haemolytic anaemia. Duration Several weeks to months. Reservoir/source Humans. Mode of Ingestion of food and water contaminated with faecal matter. Food handlers transmission and carrying the pathogen may be an important source of food contamination. example of foods Secondary transmission may also occur. involved in Examples of foods involved include prepared foods, dairy products (e.g. raw outbreaks milk), meat products, shellfish, vegetables, salads. Specific control Industrial: treatment of drinking water, and an effective sewage disposal system. measures Food service establishment/household: safe food preparation practices including careful hand-washing with soap and water, thorough cooking and reheating of food prior to consumption, disinfection of food preparation surfaces and thorough washing of all fruit and vegetables. Occurrence Predominantly in developing countries where the estimated rate of occurrence is ++. In industrialized countries the estimated rate of occurrence is +. Other comments Excretion of the organism may occur after recovery or by asymptomatic carriers, and this may be lifelong unless treated. Case–fatality rate is estimated at about 6% in industrialized countries.

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Type of illness Staphylococcus aureus intoxication

ICD code ICD-9: 005.0 ICD-10: A05.0 Etiological agent Bacterial toxin: Staphylococcus aureus enterotoxin. Characteristics of Gram-positive, non-motile, non-spore-forming facultatively anaerobic cocci. the agent Growth temperature is between 7 °C and 48 °C, with an optimum of about 37°C. They grow in a pH range of 4–9.3. Optimum pH is 7.0–7.5. The range over which enterotoxin is produced is narrower, with little toxin production

below pH 6.0. Growth will occur down to an aw of 0.83, but toxin production does not occur below 0.86. This is the most resistant bacterial pathogen with regard to decreased water activity. Intoxication is caused by a toxin which is formed in the food. The toxin is relatively heat-stable and can survive boiling for more than an hour. It is therefore possible for well-cooked food to cause illness but not contain any viable S. aureus cells. Incubation period 2–6 hours Symptoms An intoxication, sometimes of abrupt and violent onset. Severe nausea, cramps, vomiting and prostration, sometimes accompanied by diarrhoea. Duration About 2 days. Reservoir/source Humans (skin, nose, throat). S. aureus is carried by about 25–40 % of the healthy population. Mode of Consumption of foods containing the toxin. Foods are contaminated by food transmission and handlers. If storage conditions are inadequate, the bacteria may multiply to example of foods produce toxin. Intoxication is often associated with cooked food, e.g. meat, involved in where competitive bacteria have been destroyed. outbreaks Examples of foods involved include prepared foods subject to handling in their preparation (ham, chicken and egg salads, cream-filled products, ice-cream, cheese). Specific control Food service establishment/household: Exclusion of food handlers with visibly measures infected skin lesions (boils, cuts etc) from work; thorough personal hygiene of workers; prevention of time–temperature abuse in handling cooked/ready-to- eat foods. Occurrence Worldwide. The estimated rate of occurrence varies between ++ and +++ depending on conditions of food hygiene. Other comments Case–fatality rate is estimated at less than 0.02%.

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Type of illness Shigellosis (or bacillary dysentery)

ICD code ICD-9: 004 ICD-10: A03 Etiological agent Bacteria: Shigella dysenteriae, S. flexneri, S. boydii, S. sonnei. Characteristics Gram-negative, non-motile, non-spore-forming, facultatively anaerobic rods. of the agent Typically mesophilic: growing between 10 °C and 45 °C and optimally at 37 °C. The bacteria grow best in the pH range 6–8 and do not survive below pH 4.5.

The minimum aw for growth is 0.97. Incubation period 1–3 days, up to 1 week for S. dysenteriae. Symptoms Abdominal pain, vomiting, fever accompanied by diarrhoea that can range from watery (S. sonnei) to a dysenteric syndrome of bloody stools containing mucus and pus (Sh. dysenteriae and, to a lesser extent, S. flexneri and S .boydii). Sequelae In 2–3% of cases these may be: haemolytic uraemic syndrome, erythema nodosum, Reiter disease, splenic abscesses, synovitis. Duration A few days to a few weeks. Reservoir/source Humans. Mode of Food and water contaminated with faecal matter. Person-to-person transmission transmission and through the faecal–oral route is an important mode of transmission. Food can example of foods be contaminated by food handlers with poor personal hygiene or by use of involved in sewage/wastewater for fertilization. outbreaks Examples of foods involved include uncooked foods that have received extensive handling such as mixed salads and vegetables; water and raw milk. Specific control Industrial: treatment of drinking water and an effective sewage disposal system. measures Food service establishment/household: safe food preparation practices including careful hand-washing with soap and water, thorough cooking and reheating of food prior to consumption, disinfection of food preparation surfaces and thorough washing of all fruit and vegetables. Occurrence Worldwide, with a higher prevalence in developing countries. Shigellosis is a major cause of diarrhoea in infants and children under the age of 5 years, and constitutes 5–15% of diarrhoeal disease cases seen at treatment centres. S. dysenteriae type 1 has been responsible for large epidemics of severe dysentery in Central America and recently Central Africa and southern Asia. Depending on the degree of development the estimated rate of occurrence may vary between + and +++. Other comments In developing countries, S. flexneri is the most common cause of infection. However, S. dysenteriae type 1, occurring in epidemic regions, causes the most severe disease. In industrialized countries, S. sonnei is the most common species isolated, and milder illness is the norm. The disease is more severe in young children than in adults among whom many infections may be asymptomatic. The elderly and those suffering from malnutrition are particularly susceptible and may develop severe symptoms or even die. Travellers are particularly at risk. Case–fatality rate in industrialized countries is low and estimated at 0.1%.

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Type of illness Salmonellosis

ICD code ICD-9: 003 ICD-10: A02.0 Etiological agent Bacteria: non-typhoid Salmonella serotypes. Characteristics of Gram-negative, mesophilic, facultatively anaerobic, motile, non-spore-forming the agent rods. Growth can occur between 5 °C and 47 °C. Optimum growth occurs at

37°C. Minimum pH and aw for growth are 4 and 0.95 respectively. Incubation period 6–48 hours, occasionally up to 4 days. Symptoms The principal symptoms are fever, headache, nausea, vomiting, abdominal pain and diarrhoea. Sequelae Reactive arthritis, septicaemia, aortitis, cholecystitis, colitis, meningitis, myocarditis, osteomyelitis, pancreatitis, Reiter disease, rheumatoid syndromes. Duration Usually a few days to 1 week, but sometimes infection may last up to 3 weeks. Reservoir/source A wide range of domestic and wild animals, including poultry, pigs, cattle, rodents, iguanas, pets such as tortoises, turtles, chicks, dogs and cats. Also humans, i.e. patients and convalescent carriers. Mode of The main route of transmission is by ingestion of the organisms in food transmission and (milk, meat, poultry, eggs) derived from infected food animals. Food can also example of foods be contaminated by infected food handlers, pets and pests, or by cross- involved in contamination owing to poor hygiene. Contamination of food and water may outbreaks also occur from the faeces of an infected animal or person. Problems caused by initial contamination may be exacerbated by prolonged storage at temperatures at which the organism may grow. Direct person-to-person transmission may also occur during the course of the infection. Examples of foods involved include unpasteurized milk, raw eggs, poultry, meat, spices, salads, chocolate. Specific control Industrial: effective heat-processing of foods of animal origin including measures pasteurization of milk and eggs; irradiation of meat and poultry. Food service establishment/household: safe food preparation practices, including thorough cooking and reheating of food and boiling of milk; adequate refrigeration; prevention of cross-contamination, cleaning and disinfection of food preparation surfaces; exclusion of pets and other animals from food- handling areas. Consumers, particularly vulnerable groups, should avoid raw and undercooked meat and poultry, as well as raw milk and raw eggs and foods containing raw eggs. Occurrence Worldwide. Estimated rate of occurrence: ++ /+++. A drastic increase in incidence of salmonellosis, due particularly to S. Enteritidis, has occurred during the past two decades in Europe, North America, and some other countries. In Europe and North America, contaminated eggs and poultry have been the major source of infection. Other comments General susceptibility is increased by achlorhydria, antacid therapy, immunosuppressive therapy and other debilitating conditions, including malnutrition. The severity of the illness is related to serotype, the number of organisms ingested and host factors. Case–fatality rate is less than 1% in industrialized countries. Symptomless excretion of the organism can continue for several weeks or, in some cases, months.

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Type of illness Listeriosis

ICD code ICD-9: 027 ICD-10: A32 Etiological agent Bacteria: Listeria monocytogenes. Characteristics of Gram-positive, non-spore-forming, facultatively anaerobic, rods. Psychrotrophic, the agent capable of growing in a temperature range of 3–42 °C., but optimally at about

30-35 °C. The pH range for growth is 5.0–9. Minimum pH and aw for growth are 4.4 and 0.92 respectively. The bacteria are able to grow in the presence of 10% salt. Incubation period A few days to several weeks. Symptoms Influenza-like symptoms such as fever, headache and occasionally gastrointestinal symptoms. Sequelae Meningoencephalitis and/or septicaemia in newborns and adults and abortion in pregnant women. The onset of meningoencephalitis (rare in pregnant women) may be sudden with fever, intense headaches, nausea, vomiting and signs of meningeal irritation. Delirium and coma may appear early; occasionally there is collapse and shock. Duration Days–weeks. Reservoir/source Water, soil, sewage, sludge, decaying vegetables, silage and faeces of numerous wild and domestic animals. Other sources may be infected animals and people. Mode of A substantial proportion of cases of listeriosis are foodborne. Examples of transmission and foods involved include raw milk, soft cheese, meat-based paste, jellied pork example of foods tongue, raw vegetables and coleslaw. involved in outbreaks Specific control Industrial: heat treatment of milk (pasteurization, sterilization) with measures measures to ensure reduction of processing contamination risks. For ready-to-eat high- risk processed foods, reduction of all cross-contamination risks after processing. Food service establishment/household: use of pasteurized or heat-treated (boiling) milk and products made from pasteurized or heat-treated milk; refrigeration of perishable foods and consumption within a short space of time. Pre-cooked refrigerated foods should be thoroughly reheated before consumption. Avoidance of certain high risk foods e.g. soft cheese, ready-to-eat meat such as paté, and raw milk and raw milk products during pregnancy. Consumers, particularly pregnant women and other vulnerable individuals should avoid eating raw foods of animal origin, e.g. raw meat, raw milk. Pregnant women should also avoid foods which support growth of Listeria, e.g. soft cheese, pre-prepared salad, cold, smoked or raw seafood, paté. Ocurrence Estimated rate of occurrence: +. The majority of cases reported have been from Europe, North America and the islands of the Pacific. Other comments The most severe form of illness occurs in fetuses and neonates, the elderly and those who are immunocompromised. About one-third of clinical cases occur in the newborn. In adults infection occurs mainly in those aged 40 or over. Transplacental fetal infection may lead to abortion or stillbirth. Asymptomatic infection may occur at all ages. Infected individuals may shed the organisms in their stools for several months. Case–fatality rate is up to 30%; in patients who have not received adequate treatment the case–fatality rate may be as high as 70%. Pregnant women and fetuses, the elderly, and immunocompromised individuals, including those receiving treatments for cancer, are the most susceptible.

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Mode of EPEC, ETEC, EIEC infections: consumption of food and water transmission and contaminated with faecal matter. Time–temperature abuse of such food increases example of foods the risk of illness. Up to 25% of infections in infants and young children in involved in developing countries are due to E. coli, in particular ETEC and EPEC, which outbreaks are observed in 10–20 % and 1–5 % of cases at treatment centres respectively. ETEC is also a major cause of traveller’s diarrhoea in developing countries. EHEC infection is transmitted mainly through consumption of foods such as raw or undercooked ground-meat products, and raw milk, from infected animals. Faecal contamination of water and other foods, as well as cross- contamination during food preparation, will also lead to infection. Examples of foods involved include ground (minced) meat, raw milk, and vegetables. Secondary transmission (person-to-person) may also occur during the period of excretion of the pathogen which is less than a week for adults but up to 3 weeks in one-third of children affected. Specific control Industrial: treatment of drinking water, and an effective sewage disposal system. measures Food service establishment/household: specific control measures based on prevention of direct and indirect contamination of food and water with faecal matter; thorough cooking and reheating of food; and good personal hygiene. For EHEC infection, control measures include: Industrial: irradiation of meat, or thorough heat processing of meat; pasteurization/sterilization of milk; treatment of wastewater used for irrigation. Food service establishment/household: thorough cooking of meat, boiling of milk or use of pasteurized milk; separation of raw and cooked foods, hand-washing before preparation of food. Consumers should avoid eating raw or partially cooked meat and poultry and drinking raw milk. Occurrence Worldwide. E. coli infections are highly prevalent in developing countries where the estimated rate of occurrence is +++. EHEC infections are mainly reported in Argentina, Chile, Europe ( France, Germany, Italy, Sweden, UK), Japan and North America. Other comments The case–fatality rate of EPEC, ETEC, EIEC infections in industrialized countries is estimated to be less than 0.1%. The case–fatality rate of EHEC infection is about 2%. The fatality rate of E. coli infections in infants and children is much higher in developing countries. Children and the elderly are particularly vulnerable to this infection and may suffer more severely. The majority of cases of EHEC infections are reported in summer.

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Type of illness Escherichia coli infections

ICD code ICD-9: 008.0 ICD-10: A04.0–A04.3 (EPEC: A04.0; ETEC: A04.1, EIEC: A04.2; EHEC: A04.3) Etiological agent Bacteria: a) E. coli enteropathogenic (EPEC). b) E. coli enterotoxigenic (ETEC) produces two types of enterotoxins: a heat- labile toxin (LT) and a heat-stable toxin (ST). c) E. coli enteroinvasive (EIEC). d) E. coli enterohaemorrhagic (EHEC) or verocytotoxin-producing E. coli (VTEC). Characteristics Gram-negative, non-spore-forming, facultatively anaerobic rods, which belong of the agent to the family Enterobacteriaceae. Typically mesophile, the bacteria will grow from about 7–10 °C up to 50 °C, with the optimum at 37 °C; in a pH range of

4.4–8.5. Minimum aw for growth is 0.95. Most E. coli are harmless inhabitants of the gut of humans and other warm-blooded animals, however the strains mentioned above may cause diseases. EHEC is more acid-resistant than other E. coli. Incubation period a) EPEC: 1–6 days; as short as 12–36 hours. b) ETEC: 1–3 days; as short as 10–12 hours. c) EIEC: 1–3 days; as short as 10–18 hours. d) EHEC: 3–8 days, with a median of 4 days. Symptoms a) EPEC infection: enteropathogenic E. coli adhere to the mucosa and change its absorption capacity causing vomiting, diarrhoea, abdominal pain, and fever. b) ETEC infection: health effects are mediated by enterotoxins. Symptoms include diarrhoea (ranging from mild afebrile diarrhoea to a severe, cholera-like syndrome of profuse diarrhoea without blood or mucus), abdominal cramps and vomiting, sometimes leading to dehydration and shock. c) EIEC infection: inflammatory disease of the gut mucosa and submucosa caused by the invasion and multiplication of EIEC in the epithelial cells of the colon. Symptoms include fever, severe abdominal pain, vomiting and watery diarrhoea (in <10% of cases stools may become bloody and may contain mucous). d) EHEC infection: abdominal cramps, watery diarrhoea that may develop into bloody diarrhoea (haemorrhagic colitis). Fever and vomiting may also occur. Sequelae EPEC, ETEC, EIEC infections are an underlying factor of malnutrition in infants and children in developing countries. EHEC infections may result in life-threatening complications, such as haemolytic uraemic syndrome (HUS): in up to 10% of patients, particularly, young children and the elderly. HUS is characterized by acute renal failure, haemolytic anaemia and thrombocytopenia. Other sequelae include erythema nodosum and thrombotic thrombocytopenic purpura. Duration a) EPEC: days–weeks. b) ETEC: up to 5 days. c) EIEC: days–weeks. d) EHEC: days–weeks. Reservoir/source Humans are the main reservoir for EPEC, ETEC, EIEC. The reservoir for EHEC is mainly cattle.

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Type of illness Clostridium perfringens enteritis

ICD code ICD-9: 005.2 ICD-10: A05.2 Etiological agent Bacteria Clostridium perfringens (produces enterotoxin in the gut) also known as Clostridium welchii. Characteristics Gram-positive, non-motile, anaerobic, spore-forming rods that will grow in of the agent the temperature range 12–50 °C, although very slowly below 20 °C. They grow extremely quickly at optimum temperature 43–47 °C. Optimum pH is between

6 and 7, but growth will occur as low as pH 5. Lowest aw supporting growth is 0.95. Incubation period 8–24 hours. Symptoms Abdominal pain and diarrhoea. Vomiting and fever are rare. Duration 1–2 days Reservoir/source Soil, sewage, dust, faeces of animals and humans, animal-origin feedstuffs. Mode of Illness is usually caused by cooked meat and poultry dishes subject to time– transmission and temperature abuse. The dish has usually been left too long at ambient example of foods temperature for cooling before storage, or cooled inadequately. This allows involved in spores surviving the cooking process to germinate and grow, producing large outbreaks numbers of vegetative cells. If the dish is not reheated sufficiently before consumption to kill the vegetative cells then illness can result. Examples of foods involved include meat and poultry (boiled, stewed or casseroled). Specific control Food service establishment/household: adequate cooling and cool storage of cooked measures products: meat based sauces and large pieces of meat should be cooled to <10°C within 2–3 hours; thorough reheating of stored food before consumption; preparation of quantities as required when there is no available refrigeration. Occurrence Worldwide. Estimated rate of occurrence:++/ +++. Other comments Case–fatality rate in industrialized countries is very low at <0.1%.

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Type of illness Cholera

ICD code ICD-9: 001 ICD-10: A00 Etiological agent Bacteria: Vibrio cholerae O1 (enterotoxin in the gut) . Two biotypes are distinguished: classical and eltor. These are further divided in Ogawa and Inaba serotypes. Also, Vibrio cholerae O139. Characteristics of Gram-negative, facultatively anaerobic, motile, non-spore-forming rods which

the agent grow at 18–42 °C and optimally at 37 °C. Will grow down to aw 0.97 and over a pH range of 6–11; optimum pH is 7.6. Growth is stimulated by salinity levels of around 3% but is prevented at 6%. They are resistant to freezing but sensitive to heat and acid and may survive for some days on fruit and vegetables. V. cholerae is non-invasive and diarrhoea is mediated by cholera-toxin formed in the gut. Incubation period 1–3 days. Symptoms Profuse watery diarrhoea, which can lead to severe dehydration, collapse and death within a few hours unless lost fluid and salt are replaced; abdominal pain and vomiting. Duration Up to 7 days. Reservoir/source Humans. V. cholerae is often found in aquatic environments and is part of the normal flora in brackish water and estuaries. Mode of Food and water contaminated through contact with faecal matter or infected transmission and food handlers. Contamination of vegetables may occur through sewage or example of foods wastewater used for irrigation. Person-to-person transmission through the involved in faecal–oral route is also an important mode of transmission. outbreaks Examples of foods involved include seafood, vegetables, cooked rice, and ice. Specific control Industrial: control measures include safe disposal of excreta and measures sewage/wastewater; treatment of drinking-water, e.g. chlorination; irradiation, heat treatment of foods, e.g. canning. Food service establishment/household: personal hygiene (washing hands with soap and water); thorough cooking of food and careful washing of fruit and vegetables; boiling drinking-water when safe water is not available. Consumers should avoid eating raw seafood. In some countries, travellers may need to be vaccinated. Occurrence Africa, Asia, parts of Europe and Latin America. In most industrialized countries, reported cholera cases are imported by travellers, or occur as a result of import of food by travellers. Estimated rate of occurrence: in industrialized countries it occurs rarely and is mainly imported. In Africa and Central and South America, +/++ , and in other parts of the world +. Other comments In endemic areas, cholera occurs mainly in children because of lack of prior immunity; in epidemics children and adults are equally susceptible. Case–fatality rate can be less than 1% with adequate treatment; in untreated cases, the case–fatality rate may exceed 50%.

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Type of illness Campylobacteriosis

ICD code ICD-9: 008.4 ICD- 0: A04.5 Etiological agent Bacteria: Campylobacter jejuni and Campylobacter coli. Characteristics Gram-negative, non-spore-forming, curved or spiral, motile rods which are of the agent sensitive to oxygen and grow best at low oxygen levels in the presence of carbon dioxide. Optimum pH 6.5–7.5. They will not grow below 28–30 °C, grow optimally at 42–45 °C and are very sensitive to heat, salt, reduced pH levels (<6.5) and dry conditions. The organism survives better in cold conditions than ambient temperature. Incubation period 1–11 days, most commonly 2–5 days. Symptoms Fever, severe abdominal pain, nausea, and diarrhoea which can vary from slight to profuse watery diarrhoea sometimes containing blood or mucus. Sequelae Sequelae may occur in 2–10% of cases. These include reactive arthritis, Guillain– Barré syndrome, haemolytic uraemic syndrome, meningitis, pancreatitis, cholecystitis, colitis, endocarditis, erythema nodosum. Duration Up to 10 days; excretion of the organism can continue for 2–3 weeks. Reservoir/source Domestic animals (cats, dogs), livestock (pigs, cattle, sheep), birds (poultry), polluted water. Mode of Main food sources are raw milk and raw or undercooked poultry. transmission and The bacteria can be spread to other foods by cross- contamination, example of foods or contamination with untreated water, contact with animals and birds. involved in Other sources of transmission are contact with live can also occur during outbreaks the infectious period which ranges from several days to several weeks. Examples of foods involved include raw milk, poultry, beef, pork and drinking- water. Specific control Industrial: heat treatment (pasteurization/sterilization of milk); hygienic slaughter measures and processing procedures, irradiation of meat and poultry; treatment of water. Food service establishment/household: heat treatment of milk (boiling); thorough cooking of all meat; washing of salads; prevention of cross-contamination of contact surfaces; personal hygiene in food preparation (hand-washing after contact with animals); keeping pets away from food-handling areas. Consumers should avoid eating raw or partially-cooked poultry and drinking raw milk. Occurrence Worldwide. This is one of the most frequently reported foodborne diseases in industrialized countries. In developing countries it is a major cause of infant and traveller’s diarrhoea. Some 10–15% of cases of diarrhoeal disease in children seen at treatment centres are caused by Campylobacter spp. Estimated rate of occurrence: ++/+++ in industrialized and developing countries respectively. Other comments Many infections are asymptomatic. Infected individuals not treated with antibiotics may excrete the organisms for as long as 2–7 weeks. Infection is sometimes misdiagnosed as appendicitis. More sporadic cases occur in the warmer months. The case–fatality rate in industrialized countries is about 0.05%. Infants and young children are the most susceptible.

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Type of illness Brucellosis (undulant fever)

ICD code ICD-9: 023 ICD-10: A23 Etiological agent Bacteria: a) Brucella abortus b) Brucella melitensis c) Brucella suis Characteristics Gram-negative, aerobic, non-spore-forming, short, oval non-motile rods which of the agent grow optimally at 37 °C; heat-labile. Optimum pH for growth: 6.6–7.4. Incubation period Variable, from a few days to several weeks or months. Symptoms Continuous, intermittent or irregular fever, lassitude, sweat, headache, chills, constipation, body pain, weight loss and anorexia. Sequelae Bouts of fever, osteoarticular complications in 20–60% of cases, sacroiliitis, genitourinary complications (including orchitis, epididymitis, sexual impotence), cardiovascular and neurological conditions, insomnia, depression. Duration Weeks. Reservoir/source Cows, goats, pigs, sheep. a) Brucella abortus: cows. b) Brucella melitensis: sheep and goats. c) Brucella suis: pigs. Mode of Contracted principally from close association with infected animals and therefore transmission and an occupational disease of farmers, herdsmen, veterinarians and slaughterhouse example of foods workers. involved in It can also be contracted by consumption of milk usually goat’s or sheep’s outbreaks milk), and products made from unpasteurized milk, e.g. fresh goat cheese. Specific control Industrial: heat treatment of milk (pasteurization or sterilization), use of measures pasteurized milk for cheese production, ageing cheese for at least 90 days. Food service establishment/household: heat treatment of milk (boiling). Other: vaccination of animals; eradication of diseased animals (testing and slaughtering). Consumers should avoid eating/ drinking raw milk and eating cheese made with raw milk. Occurrence Worldwide, with the exception of parts of northern Europe where it occurs rarely. Incidence in North America is decreasing. Currently reported incidence in the USA is below 120 cases per year. Prevalent in eastern Mediterranean areas, southern Europe, North and East Africa, Central and Southern Asia (India), Central and South America (e.g. Mexico). Estimated rate of occurrence depending on the region: + or ++. Other comments The disease is often unrecognized and unreported. Susceptible to antibiotic treatment. Case–fatality rate may be up to 2% if the disease is untreated.

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Type of illness Botulism

ICD code ICD-9: 005.1 ICD-10: A05.1 Etiological agent Bacterial toxin: toxins of Clostridium botulinum. Characteristics Gram-positive, spore-forming, obligately anaerobic, motile rods which produce of the agent seven potent neurotoxins A–G; only A, B, E, and, infrequently F have been associated with human disease (Clostridium botulinum). Group G is named Clostridium argentinense. The toxins are potentially lethal in very small doses. They act by binding at the neuromuscular junction, blocking nerve transmission and causing flaccid paralysis. Proteolytic strains of C. botulinum producing toxin types A, B and F are mesophilic, growing over the range 10–50 °C. Non- proteolytic strains producing toxin types B, E and F are psychrotrophic and can

grow at temperaturesas low as 3.3 °C. Minimum aw for growth is 0.93–0.94 and minimum pH for growth is 4.6 (proteolytic strains) or 5.0 (non-proteolytic strains). The toxin is heat-labile and can be destroyed by adequate heat treatment (boiling for 15 minutes). Spores are resistant to normal cooking temperatures, and survive drying and freezing. Incubation period 12–36 hours although may range from a few hours to 8 days. Symptoms Vomiting, abdominal pain, fatigue, muscle weakness, headache, dizziness, ocular disturbance (blurred or double vision, dilated pupils, unreactive to light), constipation, dry mouth and difficulty in swallowing and speaking, and ultimately paralysis and respiratory or heart failure. Duration From days up to 8 months; treatment is normally the rapid administration of antitoxin, alkaline stomach washing and mechanical respiratory support. Reservoir/source Soil, marine and freshwater sediments and the intestinal tracts of fish, animals, birds and insects. Mode of Ingestion of toxin pre-formed in the food. This may occur when raw or under- transmission and processed foods are stored in conditions (temperature, aw, pH and atmosphere) example of foods allowing growth of the organism. involved in Most outbreaks are due to faulty preservation of food (particularly in homes or outbreaks cottage industries), e.g. canning, fermentation, curing, or smoking, acid or oil preservation. Examples of foods involved include vegetables, condiments (e.g. pepper), fish and fish products (type E), meat and meat products. Several outbreaks have occurred as a result of consumption of uneviscerated fish, garlic in oil and baked potatoes. Honey is suspected as a mode of transmission of infant botulism. Specific control The toxin is destroyed by boiling, however spores require a much higher mesures temperature. Industrial: heat sterilization; use of nitrites in pasteurized meat. Food service establishment/household: acid-preservation of food at a low pH (<4.6); thorough cooking of home-canned food (boil and stir for 15 minutes); refrigerated storage of food, particularly vacuum-packed, fresh or lightly cured/ smoked food. Consumers should: avoid giving honey or foods containing honey to infants; discard swollen cans. Occurrence Worldwide; particularly frequent among Alaskan populations due to faulty fermentation. Estimated rate of occurrence: +. Other comments Case–fatality rate in industrialized countries is in the range 5–10%.

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Type of illness Bacillus cereus gastroenteritis a) Diarrhoeal syndrome b) Emetic syndrome ICD code ICD-9: 005.8 ICD-10: A05.4 Etiological agent Bacterial toxin: a) Bacillus cereus diarrhoeal toxin causing toxic infection due to production of heat-labile toxins either in the gut or in food. b) Bacillus cereus emetic toxin causing intoxication due to heat-stable toxins produced in food. Characteristics of Gram-positive, facultatively anaerobic, motile rods which produce heat-resistant the agent spores; generally mesophilic, growing between 10 °C and 50 °C, with the optimum at 28–37 °C (there are, however, psychrotrophic strains which grow

at 4 °C). They will grow in a pH range of 4.3–9.3 and water activity (aw) above 0.92. Spores are moderately heat-resistant, and survive freezing and drying. Some strains require heat activation for spores to germinate and outgrow. Incubation period a) Diarrhoeal syndrome: 8–16 hours. b) Emetic syndrome: 1–5 hours. Symptoms a) Diarrhoeal syndrome: acute diarrhoea, nausea and abdominal pain. b) Emetic syndrome: acute nausea, vomiting and abdominal pain and sometimes diarrhoea. Duration a) Diarrhoeal syndrome: 24–36 hours. b) Emetic syndrome: 24–36 hours. Reservoir/source Widely distributed in nature (soil). Mode of Ingestion of food that has been stored at ambient temperatures after cooking, transmission and permitting the growth of bacterial spores and production of toxin. example of foods Many outbreaks (particularly those of emetic syndrome) are associated with involved in cooked or fried rice that has been kept at ambient temperature. outbreaks Examples of foods involved include starchy products, such as boiled or fried rice, spices, dried foods, milk and dairy products, vegetable dishes and sauces. Specific control Food service establishment/household: Effective temperature control to prevent spore measures germination and growth: food storage at >60 °C or properly refrigerated at

<10°C until use, unless other factors such as pH or aw are such as to prevent growth;When refrigeration facilities are not available, cook only quantities required for immediate consumption. Toxins associated with emetic syndrome are heat-resistant and reheating, including stir frying, will not destroy them. Occurrence Worldwide. Estimated rate of occurrence: ++/+++.

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Type of illness Aeromonas enteritis

Etiological agent Bacteria: Aeromonas hydrophila. Characteristics of Gram-negative, motile, non-spore-forming, facultatively anaerobic, straight or the agent curved rods that will not grow in 4–5% salt or at pH < 6. Optimum growth temperature is 28 °C, but growth may occur at lower temperatures, down to 4 °C. Many strains have the ability to grow over a wide pH range (4–10) under otherwise optimal conditions. Incubation period 24–48 hours. Symptoms Watery stools, stomach cramps, mild fever and vomiting. Sequelae Bronchopneumonia, cholecystitis. Duration Days–weeks. Reservoir/source A common organism found in aquatic environments that has been isolated from a wide range of foods. Mode of Seafood (fish, shrimp, oysters), snails, drinking water. transmission and example of foods involved in outbreaks Specific control Industrial: treatment and disinfection of water supplies, food irradiation. measures Food service establishment/household: thorough cooking of food, no long-term refrigeration of ready-to-eat foods. Occurrence Worldwide. Sporadic outbreaks have been reported from Africa, Australia, Europe, Japan and North America. Estimated rate of occurrence: unknown. Other comments Opportunistic pathogen.

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The following bibliographical sources have been used in the preparation of this Appendix:

Benenson AS, ed. Control of Communicable Diseases Manual: an official report of the American Public Health Association.16th ed. Washington DC, American Public Health Association, 1995.

Foodborne pathogens: risk and consequences. Task force report. Ames, USA Council of Agricultural Science and Technology, 1994.

Hobbs B, Roberts D. Food Poisoning and Food Hygiene. 6th ed. London, Edward Arnold, 1993.

Management of Outbreaks of Foodborne Illness. London, Department of Health, 1994.

Motarjemi Y, Käferstein, FK. Global Estimation of foodborne diseases. World health statistics quarterly, 1997 50(1/2): 5-11.

Quevedo F, Thakur AS. Foodborne Parasitic Diseases. Washington DC, Pan American Health Organization, 1990, (Series of scientific and technical monographs Number 12, Rev.1).

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Appendix 1

This annex is reproduced from Foodborne disease: a focus for health education (© World Health Organization, 1999). Applications and enquiries to reproduce or translate this annex should be addressed to the Office of Publications, Wold Health Organization, Geneva, Switzerland.

Causative agents of foodborne illness The following tables provide concise information about the epidemiology of foodborne diseases and how they can be prevented. The tables give the name (and alternative names) of foodborne illnesses, together with the following information about each of them:

l the code by which the illness is classified in the International classification of diseases, 9th and 10th revisions (ICD-9 and ICD-10); l the etiological agent that cause the illness; l the main characteristics of the etiological agent; l the incubation period of the illness; l the symptoms; l the sequelae that may result from the illness; l the duration of the illness; l the reservoir or source of the etiological agent; l the mode of transmission of the agent, together with examples of foods that have been involved in outbreaks; l measures that can be taken to control/prevent the spread of the etiological agent (by industry, by professional and domestic food handlers, and by consumers); l the occurrence of the illness, as indicated by +( less 1 case per 100 000 population), ++ (1-100 cases per 100 000 population) and +++ (over 100 case per 100 000 population); l the geographical occurrence of the illness; l other details about the nature of the illness or about the agent that causes it.

The diseases are listed in alphabetical order by type of pathogen, with bacteria first, then viruses and then parasites (protozoa, nematodes, cestodes, and trematodes).